Process for making a voltage dependent resistor

ABSTRACT

A process for making a bulk-type voltage-dependent resistor and more particularly to a varistor comprising a zinc oxide sintered body using heat-treated zinc oxide powder. By heat-treating zinc oxide powder before the sintering step, a bulk-type voltage-dependent resistor is obtainable which is characterized by a high n-value in a region of current higher than 10A/cm 2  and high power dissipation as well as a lower C-value.

This invention relates to a process for making voltage dependentresistors (varistors) having non-ohmic resistance (voltage-dependentproperty) due to the bulk thereof and more particularly tovoltage-dependent resistors, which are suited e.g. for surge absorbersusing heat-treated zinc oxide, and additives.

Various voltage-dependent resistors such as silicon carbidevoltage-dependent resistors, selenium rectifiers and germanium orsilicon p-n junction diodes have been widely used for stabilization ofvoltage of electrical circuits or suppression of abnormally high surgeinduced in electrical circuits. The electrical characteristics of suchvoltage-dependent resistors are expressed by the relation: ##EQU1##where V is the voltage across the resistor, I is the current flowingthrough the resistor, C is a constant corresponding to the voltage at agiven current and exponent n is a numerical value greater than 1. Thevalue of n is calculated by the following equation: ##EQU2## where V₁and V₂ are the voltage at given currents I₁ and I₂, respectively. Thedesired value of C depends upon the kind of application to which theresistor is to be put. It is ordinarily desirable that the value of n beas large as possible since this exponent determines the extent to whichthe resistors depart from ohmic characteristics. Conveniently the,n-value defined by I₁, I₂, V₁ and V₂ as shown in equation (2) isexpressed by ₁ n₂ for distinguishing from the n-value calculated byother currents or voltages.

Voltage-dependent resistors comprising sintered bodies of zinc oxidewith or without additives and non-ohmic electrodes applied thereto, havealready been disclosed as seen in U.S. Pat. Nos. 3,496,512, 3,570,002,3,503,029, 3,689,863 and 3,766,098. The nonlinearity (voltage-dependentproperty) of such voltage-dependent resistors is attributed to theinterface between the sintered body of zinc oxide with or withoutadditives and a silver paint electrode, and is controlled mainly bychanging the compositions of the sintered body and the silver paintelectrode. Therefore, it is not easy to control the C-value over a widerange after the sintered body is prepared. Similarly, involtage-dependent resistors comprising germanium or silicon p-n junctiondiodes, it is difficult to control the c-value over a wide range becausethe nonlinearity of these voltage-dependent resistors is not attributedto the bulk but rather to the p-n junction. In addition, it is almostimpossible for those zinc oxide voltage-dependent resistors mentionedabove and germanium or silicon diode voltage-dependent resistors to havea combination of a C-value higher than 100 volt, an n-value higher than10 and high surge resistance tolerable for a surge of more than 100A.

On the other hand, the silicon carbide voltage-dependent resistors havenonlinearity due to the contacts among the individual grains of siliconcarbide bonded together by a ceramic binding material, i.e. to the bulk,and the C-value is controlled by changing a dimension in the directionin which the current flows through the voltage-dependent resistors. Inaddition, the silicon carbide voltage-dependent resistors have highsurge resistance thus rendering them suitable e.g. as surge absorbersand as characteristic elements of lightning arresters. Thecharacteristic elements are used usually by connecting them in serieswith discharging gaps and determine the level of the discharging voltageand the follow current. However, the silicon curbide varistors, have arelatively low n-value ranging from 3 to 7 which results in poorsuppression of lightning surge or increase in the follow current.Another defect of the arrester with a discharging gap is slow responseto surge voltage a very short rise time such as below 1μs. It isdesirable for the arrester to surpress the lightning surge and thefollow current to a level as low as possible and respond to surgevoltage instantaneously. The silicon carbide voltage-dependentresistors, however, have a relatively low n-value ranging from 3 to 7which results in poor surge suppression.

There have been known, on the other hand, voltage-dependent resistors ofthe bulk type comprising a sintered body of zinc oxide with additives,as seen in U.S. Pat. Nos. 3,633,458, 3,632,529, 3,634,337, 3,598,763,3,682,841, 3,642,664, 3,658,725, 3,687,871, 3,723,175, 3,778,743,3,806,765 3,811,103 and copending U.S. Pat. application Nos. 29,416,388,169, now U.S. Pat. No. 3,863,193, 428,737, now U.S. Pat. No.3,872,582 and 489,827. These zinc oxide voltage-dependent resistors ofthe bulk type contain, as additives, one or more combinations of oxidesor fluorides of bismuth, cobalt, manganese, barium, boron, berylium,magnesium, calcium, strontium, titanium, antimony, germanium, chromiumand nickel, and the C-value is by changing, mainly, the compositions ofsaid sintered body and the distance between electrodes and they have anexcellent voltage-dependent properties for in an n-value in a region ofcurrent less than 10A/cm². For a current higher than 10A/cm², however,the n-value goes down to a value lower than 10. This defect of thesezinc oxide voltage-dependent resistors of bulk type is presumably mainlydue to their low n-value for the lower C-value, especially less than 70volts. In general, these zinc oxide voltage-dependent resistors of thebulk type, mentioned above, have a very low n-value i.e. less than 20,when the C-value is lower than 70 volts. The development of thevoltage-dependent resistors having a C-value less than 70 volts has beenrequired for the application to low voltage circuits, such as in theautomobile industry and home appliances, but the n-value of aconventional voltage-dependent resistor having such a lower C-value istoo small for uses such as voltage stabilizers and surge absorbers. Forthese reasons, voltage-dependent resistors of this type having a C-valueless than 70 volts have been used infrequently in the low voltageapplications.

An object of the present invention is to provide a method for making abulk-type voltage dependent resistor characterized by a high n-value ina region of current higher than 10A/cm² and a high power dissipation forsurge impulse.

Another object of the present invention is to provide a method formaking a bulk-type voltage-dependent resistor having a lower C-value.

These and other objects of this invention will become apparent uponconsideration of the following detailed description taken together withthe accompanying drawing in which the single FIGURE is a cross-sectionalview of a voltage dependent resistor in accordance with this invention.

Before proceeding with a detailed description of the manufacturingprocess of the voltage-dependent resistor contemplated by thisinvention, its construction will be described with reference to thesingle FIGURE wherein reference numeral 10 designates, as a whole, avoltage-dependent resistor comprising, as its active element, a sinteredbody having a pair of electrodes 2 and 3 in an ohmic contact with toopposite surfaces thereof. The sintered body 1 is prepared in a mannerhereinafter set forth and is any form such as circular, square orrectangular plate form. Wire leads 5 and 6 are attached conductively tothe electrodes 2 and 3, respectively, by a connection means 4 such assolder or the like. According to this invention, a process for making abulk-type voltage-dependent resistor comprising a sintered bodyconsisting essentially of, as a major part, zinc oxide (ZnO), andadditives, and having electrodes to the opposite surfaces of saidsintered body, characterized by a high n-value in a region of currenthigher than 10A/cm², a high power dissipation for a surge pulse and alow C-value, especially less than 70 volts, comprises heat-treating ofthe zinc oxide powder used for the sintered body at a temperaturebetween 500°C and 1000°C.

It has been discovered according to the invention that the n-value bothin a region of current more than 10A/cm² and in a region of currentbetween 0.1mA and 1mA, the power dissipation for a surge pulse and a lowC-value, especially, less than 70 volts, are further improved when saidheat-treating temperature of the zinc oxide powder is between 700°C and800°C. A composition for use as said zinc oxide sintered body havingvoltage dependent properties by itself, according to the presentinvention, can be prepared by using those of described in U.S. Pat. Nos.3,633,458, 3,632,529, 3,634,337, 3,598,763, 3,682,841, 3,642,664,3,648,725, 3,687,871, 3,723,175, 3,778,743, 3,806,765, 3,811,103 andcopending U.S. Pat. applications Nos. 29,416, 388,169, now U.S. Pat. No.3,863,193, 428,737, now U.S. Pat. No. 3,872,582 and 489,827. Amongvarious compositions, a more desirable result can be obtained with acomposition consisting essentially of, as a main constituent, 99.98 to80 mole percent of zinc oxide (ZnO), and, as additives, 0.01 to 10 molepercent of bismuth oxide (Bi₂ O₃), and 0.01 to 10 mole percent, intotal, of two members selected from the group consisting of cobalt oxide(CoO), uranium oxide (UO₂), manganese oxide (MnO), antimony oxide (Sb₂O₃), barium oxide (BaO), strontium oxide (SrO) and lead oxide (PbO).

It has been discovered according to the present invention that a highern-value both in a region of current higher than 10A/cm² and in a currentregion between 0.1mA and 1mA, a higher power dissipation for a surgepulse and a lower C-value can be obtained when said sintered bodycomprises, as a main constitutent, zinc oxide (ZnO), and, as additives,0.01 to 10 mole percent of bismuth oxide (Bi₂ O₃), 0.1 to 3.0 molepercent of cobalt oxide (CoO), 0.1 to 3.0 mole percent of manganeseoxide (MnO) and at least one member selected from the group consistingof 0.01 to 8.0 mole percent of antimony oxide (Sb₂ O₃), 0.1 to 5.0 molepercent of tin oxide (SnO₂) and 0.02 to 10 mole percent of silicon oxide(SiO₂) and at least one member selected from the group consisting of0.01 to 5.0 mole percent of chromium oxide (Cr₂ O₃) and 0.01 to 5.0 molepercent of nickel oxide (NiO), and said heat-treating temperature ofzinc oxide powder is between 500°C and 1000°C.

The n-value both in a region of current higher than 10A/cm² and in aregion of current between 0.1 mA and 1 mA, the power dissipation for asurge pulse and the C-value of less than 70 volts are further improvedwhen said sintered body comprises, as a main constituent, zinc oxide(ZnO), and, as additives, 0.01 to 5.0 mole percent of bismuth oxide (Bi₂O₃), 0.1 to 3.0 mole percent of cobalt oxide (CoO), 0.1 to 3.0 molepercent of manganese oxide (MnO) and at least one member selected fromthe group consisting of 0.1 to 3.0 mole percent of titanium oxide(TiO₂), 0.01 to 5.0 mole percent of nickel oxide (NiO), 0.01 to 5.0 molepercent of chromium oxide (Cr₂ O₃), 0.01 to 5.0 mole percent of bariumoxide (BaO) and 0.01 to 5.0 mole percent of boron oxide (B₂ O₃), andsaid heat-treating temperature of zinc oxide powder is between 500°C and1000°C.

It has been discovered according to the present invention that then-value both in a region of current higher than 10A/cm² and in a regionof current between 0.1mA and 1mA, the power dissipation for a surgepulse and the C-value have been remarkably improved when saidheat-treating temperature of zinc oxide powder is between 700°C and800°C and said sintered body comprises, as a main constituent, zincoxide (ZnO), and, as additives, either 0.01 to 10 mole percent ofbismuth oxide (Bi₂ O₃), 0.1 to 3.0 mole percent of cobalt oxide (CoO),0.1 to 3.0 mole percent of manganese oxide (MnO) and at least one memberselected from the group consisting of 0.01 to 8.0 mole percent ofantimony oxide (Sb₂ O₃), 0.1 to 5.0 mole percent of tin oxide (SnO₂),and 0.01 to 10 mole percent of silicon oxide (SiO₂), and at least onemember selected from the group consisting of 0.01 to 5.0 mole percent ofchromium oxide (Cr₂ O₃), 0.01 to 5.0 mole percent of nickel oxide (Nio),or 0.01 to 5.0 mole percent of bismuth oxide (Bi₂ O₃), 0.1 to 3.0 molepercent of cobalt oxide (CoO), 0.1 to 3.0 mole percent of manganeseoxide (MnO) and at least one member selected from the group consistingof 0.1 to 3.0 mole percent of titanium oxide (TiO₂), 0.01 to 5.0 molepercent of nickel oxide (NiO), 0.01 to 5.0 mole percent of chromiumoxide (Cr₂ O₃), 0.01 to 5.0 mole percent of barium oxide (BaO) and 0.01to 5.0 mole percent of boron oxide (B₂ O₃).

The heat-treating process for the zinc oxide powder can be carried outby any suitable and available method such as firing said zinc oxidepowder which is packed in a alumina crucible or sagger at a givenheat-treating temperature between 500°C and 1000°C for a given time.Said zinc oxide powder used is a high grade or industrial grade zincoxide and it contains less than 0.01 mole percent of impurity (withoutany dopant) added before the heat-treating process. It is not alwaysadvantageous that calcination of the mixture of zinc oxide with one ormore additives be carried out. The heat-treating of the zinc oxidepowder before mixing the zinc oxide and the additives is necessary toachieve the higher n-value both in a region of current higher than10A/cm and in a region of current between 0.1mA and 1mA, the higherpower dissipation for a surge pulse and the lower C-value which are theadvantages of the present invention.

The sintered body 1 can be prepared by a per se well known ceramictechnique. The starting materials in the compositions in the foregoingdescription are mixed in a wet mill so as to produce homegeneousmixtures. The mixtures are dried and pressed in a mold into desiredshapes at a pressure from 50 kg./cm² to 500 kg/cm². The pressed bodiesare sintered in air at 1000°C to 1450°C for 1 to 20 hours, and thenfurnace-cooled to room temperature (about 15°C to about 30°C). Themixture can be preliminarily calcined at 600 to 1000°C and pulverizedfor easy fabrication in a subsequent pressing step. The mixture to bepressed can be admixed with a suitable binder such as water, polyvinylalcohol, etc. It is advantageous that the sintered body be lapped at theopposite surfaces by abrasive powder such as silicon carbide with aparticle size of about 10 to 50μ in mean diameter. The sintered bodiesare provided, at the opposite surfaces thereof, with electrodes in anyavailable and by any suitable method such as silver painting, vacuumevaporation or flame spraying of metal such as Al, Zn, Sn, etc.

The voltage-dependent properties are not affected in a practical way bythe kind of electrodes used, but are affected by the thickness of thesintered bodies. Particularly, the C-value varies in proportion to thethickness of the sintered bodies, while the n-value is almostindependent of the thickness. This surely means that thevoltage-dependent property is due to the bulk itself, but not to theelectrodes.

Lead wires can be attached to the electrodes in a per se conventionalmanner by using conventional solder. It is convenient to employ aconductive adhesive comprising silver powder and resin in an organicsolvent in order to connect the lead wires to the electrodes.Voltage-dependent resistors according to this invention have a highstability in a surge test which is carried out by applying a surge wavehaving a form of 8×20μsec and 1000A/cm². The n-value does not changesignificantly after the heating cycles, the load life test, a humiditytest and a surge life test. It is advantageous for achievement of highstability with respect to humidity that the resultant voltage-dependentresistors be embedded in a humidity proof resin such as epoxy resin andphenol resin in a per se well known manner.

The following examples are meant to illustrate preferred embodiments ofthis invention, but not meant to limit the scope thereof.

EXAMPLE 1

Zinc oxide was heat-treated in air for 2 hours at the temperatureslisted in Table 1. The slurry was dried and pressed in a mold into discs17.5 mm in diameter and 2 mm in thickness at a pressure of 250 kg/cm².The pressed bodies were sintered in air at temperatures listed in Table1 and then furnace-cooled to room temperature. The zinc oxide sinteredbodies were lapped on the opposite surfaces thereof to a thickness of 1mm by silicone carbide abrasive having particle size of 30 μ in meandiameter. The opposite surfaces of the sintered body were provided witha spray metallized film of aluminum by a per se well known technique.

The electrical characteristics of the resultant sintered bodies areshown in Table 1. The zinc oxide sintered bodies have an ohmic propertyand have a specific resistivity less than 3Ω-cm. It is easily understoodthat the heat-treating temperature between 700°C and 800°C is preferablefor lower specific resistivity.

                                      Table 1                                     __________________________________________________________________________                  Sintering                                                       Heat-treating tempera-     Specific resislivity                               ture of zinc oxide powder                                                                   Tempera-     of zinc oxide sintered                             (°C)   ture (°C)                                                                     Time (hr)                                                                           body (Ω-cm)                                  __________________________________________________________________________                  1000   20    2.5                                                              1200   10    1.2                                                500           1350   2     0.9                                                              1450   1     0.3                                                              1000   20    0.5                                                              1200   10    0.3                                                600           1350   2     0.25                                                             1450   1     0.12                                                             1000   20    0.09                                                             1200   10    0.08                                               700           1350   2     0.06                                                             1450   1     0.06                                                             1000   20    0.07                                                             1200   10    0.07                                               750           1350   2     0.06                                                             1450   1     0.05                                                             1000   20    0.08                                                             1200   10    0.07                                               800           1350   2     0.06                                                             1450   1     0.06                                                             1000   20    0.5                                                              1200   10    0.3                                                900           1350   2     0.2                                                              1450   1     0.09                                                             1000   20    3.0                                                              1200   10    1.0                                                1000          1350   2     0.7                                                              1450   1     0.3                                                __________________________________________________________________________

EXAMPLE 2

Zinc oxide powder was heat-treated, first of all, under the conditionlisted in Table 2. The heat-treated zinc oxide was pulverized and driedby the same process as that of Example 1. The heat-treated zinc oxidefine powder and additives listed in Table 2 were mixed in a wet mill for24 hours. The mixture was dried and pressed in a mold into discs 17.5 mmin diameter and 25 mm in thickness at a pressure of 250 kg/cm².

The pressed bodies were sintered in air under the conditions shown inTable 2, and then furnace-cooled to room temperature. The sinteredbodies were lapped on the opposite surfaces thereof to a thickness shownin Table 2 by silicon carbide abrasive having a particle size of 30μ inmean diameter. The opposite surfaces of the sintered bodies wereprovided with a spray metallized film of aluminum by a per se well knowntechnique.

The electric characteristics of the resultant sintered bodies are shownin Table 2, which shows that the C-value varies approximately inproportion to the thickness of the sintered body while the n-value isessentially independent of the thickness. It will be readily recognizedthat the voltage-dependent property of the sintered body is attributedto the sintered body itself.

                                      Table 2                                     __________________________________________________________________________    Heat-treating of                                                                         Composition                   Electrical properties                zine oxide powder                                                                        (mole %)     Sintering  Thickness                                                                           of resultant resistor                                                         C at a given                         Temperature                                                                          Time             Temperature                                                                          Time                                                                              (mm)  current of                           (°C)                                                                          (hrs.)                                                                            ZnO Additive (°C)                                                                          (hrs.)    1mA (V)                                                                              0.1mA.sup.n 1mA               __________________________________________________________________________    750    2   99.5                                                                              Bi.sub.2 O.sub.3                                                                   0.5 1000   3   20    730    9.2                           750    2   99.5                                                                              Bi.sub.2 O.sub.3                                                                   0.5 1200   1   10    360    9.1                           750    2   99.5                                                                              Bi.sub.2 O.sub.3                                                                   0.5 1200   1   3     110    9.0                           500    10  99.5                                                                              Bi.sub.2 O.sub.3                                                                   0.5 1200   1   20    750    8.8                           700    2   99.5                                                                              Bi.sub.2 O.sub.3                                                                   0.5 1200   1   20    733    9.2                           800    2   99.5                                                                              Bi.sub.2 O.sub.3                                                                   0.5 1200   1   20    740    9.2                           1000   1   99.5                                                                              Bi.sub.2 O.sub.3                                                                   0.5 1200   1   20    790    8.9                           750    2   97.0                                                                              Bi.sub.2 O.sub.3                                                                   3.0 1200   3   1     40     9.3                           750    2   97.0                                                                              Bi.sub.2 O.sub.3                                                                   3.0 1200   3   3     120    9.5                           750    2   97.0                                                                              Bi.sub.2 O.sub.3                                                                   3.0 1200   3   10    400    9.7                           500    10  97.0                                                                              Bi.sub.2 O.sub.3                                                                   3.0 1200   3   20    815    9.8                           700    2   97.0                                                                              Bi.sub.2 O.sub.3                                                                   3.0 1200   3   20    800    10.2                          800    2   97.0                                                                              Bi.sub.2 O.sub.3                                                                   3.0 1200   3   20    800    10.3                          1000   1   97.0                                                                              Bi.sub.2 O.sub.3                                                                   3.0 1200   3   20    820    9.9                           750    2   99.5                                                                              CoO  0.5 1000   2   1     96     5.0                           750    2   99.5                                                                              CoO  0.5 1000   2   3     290    5.0                           750    2   99.5                                                                              CoO  0.5 1000   2   10    965    5.2                           750    2   99.5                                                                              CoO  0.5 1000   2   20    1930   5.4                           500    20  97.0                                                                              CoO  3.0 1100   1   20    260    4.0                           700    2   97.0                                                                              CoO  3.0 1100   1   20    220    4.5                           800    2   97.0                                                                              CoO  3.0 1100   1   20    220    4.7                           1000   1   97.0                                                                              CoO  3.0 1100   1   20    240    4.0                           750    2   99.5                                                                              UO.sub.2                                                                           0.5 1350   1   1     40     6.1                           750    2   99.5                                                                              UO.sub.2                                                                           0.5 1350   1   3     122    6.4                           750    2   99.5                                                                              UO.sub.2                                                                           0.5 1350   1   10    400    6.6                           750    2   99.5                                                                              UO.sub.2                                                                           0.5 1350   1   20    805    6.8                           750    2   95.0                                                                              SnO.sub.2                                                                          5.0 1300   1   1     7      3.4                           750    2   95.0                                                                              SnO.sub.2                                                                          5.0 1300   1   3     20     3.5                           750    2   95.0                                                                              SnO.sub.2                                                                          5.0 1300   1   10    67     3.7                           750    2   95.0                                                                              SnO.sub.2                                                                          5.0 1300   1   20    130    3.8                           750    2   99.5                                                                              MnO  0.5 1200   1   1     127    6.6                           750    2   99.5                                                                              MnO  0.5 1200   1   3     380    6.6                           750    2   99.5                                                                              MnO  0.5 1200   1   10    1270   6.7                           500    10  99.5                                                                              MnO  0.5 1200   1   20    1300   5.9                           700    2   99.5                                                                              MnO  0.5 1200   1   20    1275   6.6                           800    2   99.5                                                                              MnO  0.5 1200   1   20    1279   6.6                           1000   1   99.5                                                                              MnO  0.5 1200   1   20    1340   5.7                           750    2   97.0                                                                              MnO  3.0 1000   5   20    3170   6.0                           750    2   97.0                                                                              MnO  3.0 1200   2   3     480    7.5                           750    2   97.0                                                                              MnO  3.0 1200   2   10    1580   6.7                           500    10  97.0                                                                              MnO  3.0 1200   2   20    3300   6.0                           700    2   97.0                                                                              MnO  3.0 1200   2   20    3200   6.7                           800    2   97.0                                                                              MnO  3.0 1200   2   20    3210   6.7                           1000   1   97.0                                                                              MnO  3.0 1200   2   20    3360   5.9                           750    5   99.5                                                                              Sb.sub.2 O.sub.3                                                                   0.5 1000   3   20    1070   4.2                           750    5   99.5                                                                              Sb.sub.2 O.sub.3                                                                   0.5 1200   1   3     162    4.0                           750    5   99.5                                                                              Sb.sub.2 O.sub.3                                                                   0.5 1200   1   10    535    4.0                           500    10  99.5                                                                              Sb.sub.2 O.sub.3                                                                   0.5 1200   1   20    1100   3.7                           700    5   99.5                                                                              Sb.sub.2 O.sub.3                                                                   0.5 1200   1   20    1075   4.1                           800    5   99.5                                                                              Sb.sub.2 O.sub.3                                                                   0.5 1200   1   20    1080   4.1                           1000   2   99.5                                                                              Sb.sub.2 O.sub.3                                                                   0.5 1200   1   20    1150   3.9                           750    5   97.0                                                                              Sb.sub.2 O.sub.3                                                                   3.0 1200   2   1     108    3.9                           750    5   97.0                                                                              Sb.sub.2 O.sub.3                                                                   3.0 1200   2   3     325    3.9                           750    5   97.0                                                                              Sb.sub.2 O.sub.3                                                                   3.0 1200   2   10    1085   3.9                           500    10  97.0                                                                              Sb.sub.2 O.sub.3                                                                   3.0 1200   2   20    2200   3.0                           700    5   97.0                                                                              Sb.sub.2 O.sub.3                                                                   3.0 1200   2   20    2170   3.9                           800    5   97.0                                                                              Sb.sub.2 O.sub.3                                                                   3.0 1200   2   20    2170   3.9                           1000   2   97.0                                                                              Sb.sub.2 O.sub.3                                                                   3.0 1200   2   20    2220   3.1                           750    2   99.5                                                                              BaO  0.5 1100   3   20    650    10.6                          750    2   99.5                                                                              BaO  0.5 1300   1   3     98     10.5                          750    2   99.5                                                                              BaO  0.5 1300   1   10    320    10.7                          500    10  99.5                                                                              BaO  0.5 1300   1   20    700    9.5                           700    2   99.5                                                                              BaO  0.5 1300   1   20    650    10.4                          800    2   99.5                                                                              BaO  0.5 1300   1   20    650    10.4                          1000   1   99.5                                                                              BaO  0.5 1300   1   20    710    9.2                           750    2   97.0                                                                              BaO  3.0 1300   2   1     96     7.7                           750    2   97.0                                                                              BaO  3.0 1300   2   2     295    7.8                           750    2   97.0                                                                              BaO  3.0 1300   2   10    980    7.8                           500    10  97.0                                                                              BaO  3.0 1300   2   20    2005   6.9                           700    2   97.0                                                                              BaO  3.0 1300   2   20    1970   7.5                           800    2   97.0                                                                              BaO  3.0 1300   2   20    1972   7.5                           1000   1   97.0                                                                              BaO  3.0 1300   2   20    2010   6.8                           750    5   99.5                                                                              SrO  0.5 1100   5   20    469    8.2                           750    5   99.5                                                                              SrO  0.5 1300   1   3     71     8.0                           750    5   99.5                                                                              SrO  0.5 1300   1   10    235    8.2                           500    10  99.5                                                                              SrO  0.5 1300   1   20    510    7.5                           700    5   99.5                                                                              SrO  0.5 1300   1   20    470    8.1                           800    5   99.5                                                                              SrO  0.5 1300   1   20    470    8.1                           1000   2   99.5                                                                              SrO  0.5 1300   1   20    505    7.6                           750    5   97.0                                                                              SrO  3.0 1300   2   1     58     6.5                           750    5   97.0                                                                              SrO  3.0 1300   2   3     175    6.6                           750    5   97.0                                                                              SrO  3.0 1300   2   10    578    6.6                           500    10  97.0                                                                              SrO  3.0 1300   2   20    1200   5.5                           700    5   87.5                                                                              SrO  3.0 1300   2   20    1170   6.5                           800    5   97.0                                                                              SrO  3.0 1300   2   20    1172   6.4                           1000   2   97.0                                                                              SrO  3.0 1300   2   20    1230   5.3                           750    2   99.5                                                                              PbO  0.5 1100   5   20    1315   9.4                           750    2   99.5                                                                              PbO  0.5 1300   1   3     1995   9.2                           750    2   99.5                                                                              PbO  0.5 1300   1   10    6584   9.3                           500    10  99.5                                                                              PbO  0.5 1300   1   20    1400   8.5                           700    2   99.5                                                                              PbO  0.5 1300   1   20    1320   8.3                           800    2   99.5                                                                              PbO  0.5 1300   1   20    1322   9.3                           1000   1   99.5                                                                              PbO  0.5 1300   1   20    1420   8.2                           750    2   97.0                                                                              PbO  3.0 1300   2   1     640    8.3                           750    2   97.0                                                                              PbO  3.0 1300   2   3     1920   8.5                           750    2   97.0                                                                              PbO  3.0 1300   2   10    6405   8.6                           500    10  97.0                                                                              PbO  3.0 1300   2   20    1400   7.2                           700    2   97.0                                                                              PbO  3.0 1300   2   20    1290   8.5                           800    2   97.0                                                                              PbO  3.0 1300   2   20    1289   8.4                           1000   1   97.0                                                                              PbO  3.0 1300   2   20    1380   7.6                           __________________________________________________________________________

EXAMPLE 3

Zinc oxide and additives of Table 3 were fabricated intovoltage-dependent resistors by the same process as that of Example 2.The electrical properties of the resultant resistors are shown in Table3 in which the values of n₁ and n₂ are the n-value defined between 0.1mAand 1mA, and between 10A and 100A, respectively. The thickness is 1mm.The change rates of C and n-values after an impulse test are also shownin Table 3. The impulse test is carried out by applying 2 impulses of8×20 μs, 1000A. It will be readily recognized that the heat-treating ofzinc oxide powder results in the high n-value, low C-value and smallchange rates, especially for a C-value lower than 70 volts.

                                      Table 3                                     __________________________________________________________________________    Heat-treating                                                                          Additives     Sintering                                                                             Electrical characteristics                                                                   change Rate after Impulse       of zinc oxide                                                                          (mole%)               of Resultant Resistor                                                                        Test (%)                        powder                                                                        __________________________________________________________________________                                   C (At a given) ΔC (at a given            Temp.                                                                              Time                                                                              Bi.sub.2 O.sub.3                                                                   other    Temp.                                                                             Time                                                                              current of 1mA                                                                         n.sub.1                                                                          n.sub.2                                                                          current of                                                                             Δn.sub.1                                                                    Δn.sub.2                                                                4                  (°C)                                                                        (hrs.)   additives                                                                              (°C)                                                                       (hrs.)                                                                            (V)            (V)                             __________________________________________________________________________    750  2   0.01 CoO 0.1  1300                                                                              1   20       8  6  -19      -18 -9.2               750  2   0.1  CoO 0.5  1300                                                                              1   27       13 11 -18      -19 -9.5               750  2   0.5  CoO 0.5  1300                                                                              1   35       17 15 -17      -17 -7.1               750  2   1.0  CoO 0.5  1300                                                                              1   41       15 12 -19      -19 -9.3               750  2   10.0 CoO 10.0 1300                                                                              2   61       9  7  -18      -19 -9.5               500  10  0.5  CoO 0.5  1300                                                                              1   40       15 13 -17      -18 -8.9               700  2   0.5  CoO 0.5  1300                                                                              1   36       17 14 -17      -17 -8.2               800  2   0.5  CoO 0.5  1300                                                                              1   37       17 14 -17      -17 -8.3               1000 1   0.5  CoO 0.5  1300                                                                              1   43       15 13 -17      -18 -8.9               500  10  0.5  PbO 0.5  1300                                                                              1   730      7  5  -19      -19 -9.2               700  5   0.5  PbO 0.5  1300                                                                              1   650      8  6  -16      -17 -8.3               800  5   0.5  PbO 0.5  1300                                                                              1   645      8  6  -17      -16 -8.4               1000 2   0.5  PbO 0.5  1300                                                                              1   750      7  5  -18      -19 -9.1               750  2   0.01 MnO 0.1  1300                                                                              1   19       6  6  -20      -19 -9.3               750  2   0.1  MnO 0.5  1300                                                                              1   129      11 9  -19      -20 -9.2               750  2   0.5  MnO 0.5  1300                                                                              1   64       17 15 -16      -15 -8.1               750  2   1.0  MnO 0.5  1300                                                                              1   146      7  6  -18      -19 -9.3               750  2   10.0 MnO 10.0 1300                                                                              2   230      6  4  -19      -18 - 9.4              500  10  0.5  MnO 0.5  1300                                                                              1   80       14 12 -17      -17 -8.4               700  2   0.5  MnO 0.5  1300                                                                              1   65       16 15 -16      -15 -8.1               800  2   0.5  MnO 0.5  1300                                                                              1   68       16 15 -16      -15 -8.2               1000 1   0.5  MnO 0.5  1300                                                                              1   75       12 10 -17      -17 -8.5               750  2   0.5  Sb.sub.2 O.sub.3                                                                  0.1  1350                                                                              1   25       16 14 -18      -17 -9.7               750  2   0.01 Sb.sub.2 O.sub.3                                                                  0.01 1350                                                                              1   43       14 12 -18      -17 -9.6               750  2   0.1  Sb.sub.2 O.sub.3                                                                  1.0  1350                                                                              1   52       19 15 -19      -19 -9.5               750  2   0.5  Sb.sub.2 O.sub.3                                                                  1.0  1350                                                                              1   63       20 17 -15      -15 -8.0               750  2   1.0  Sb.sub.2 O.sub.3                                                                  1.0  1350                                                                              1   70       21 15 -17      -18 -9.4               750  2   10.0 Sb.sub.2 O.sub.3                                                                  1.0  1350                                                                              2   80       23 16 -19      -20 -9.3               750  2   10.0 Sb.sub.2 O.sub.3                                                                  10.0 1350                                                                              2   90       25 16 -20      -19 -9.2               500  5   0.5  Sb.sub.2 O.sub.3                                                                  1.0  1350                                                                              1   70       78 15 -16      -16 -8.2               700  2   0.5  Sb.sub.2 O.sub.3                                                                  1.0  1350                                                                              1   65       19 17 -15      -15 -8.1               800  2   0.5  Sb.sub.2 O.sub.3                                                                  1.0  1350                                                                              1   65       19 17 -15      -15 -8.1               1000 1   0.5  Sb.sub.2 O.sub.3                                                                  1.0  1350                                                                              1   72       17 15 -17      -16 -8.4               750  2   0.5  Sb.sub.2 O.sub.3                                                                  0.01 1350                                                                              1   51       13 12 -18      -19 -9.5               750  2   0.5  BaO 0.1  1350                                                                              1   50       14 12 -19      -19 -9.4               750  2   0.5  BaO 0.5  1350                                                                              1   60       16 14 -16      -16 -7.9               750  2   0.5  BaO 2.0  1350                                                                              1   72       18 16 -19      -20 -9.1               750  2   0.5  BaO 10.0 1350                                                                              1   85       20 18 -19      -20 -9.5               500  10  0.5  BaO 0.5  1350                                                                              1   65       15 15 -16      -17 -8.1               700  2   0.5  BaO 0.5  1350                                                                              1   62       15 13 -16      -16 -7.9               800  2   0.5  BaO 0.5  1350                                                                              1   61       15 14 -16      -16 -7.9               1000 1   0.5  BaO 0.5  1350                                                                              1   65       14 12 -16      -18 -8.0               750  2   0.01 SrO 0.01 1350                                                                              1   24       7  5  -20      -19 -9.7               750  2   0.1  SrO 0.5  1350                                                                              1   30       7  5  -20      -20 -9.8               750  2   0.5  SrO 0.5  1350                                                                              1   4        10 6  -15      -16 -7.5               750  2   1.0  SrO 0.5  1350                                                                              1   14       7  5  -18      -19 -9.5               750  2   10.0 SrO 0.5  1350                                                                              1   23       7  5  -19      -20 -9.8               750  2   10.0 SrO 10.0 1350                                                                              2   42       7  5  -19      -20 -9.9               500  10  0.5  SrO 0.5  1350                                                                              1   5        9  4  -16      -17 -7.6               700  2   0.5  SrO 0.5  1350                                                                              1   4        10 5  -15      -16 -7.4               800  2   0.5  SrO 0.5  1350                                                                              1   4        10 5  -15      -16 -7.4               1000 2   0.5  SrO 0.5  1350                                                                              1   5        9  4  -16      -17 -7.8                             CoO 0.5                                                         750  2   0.5           1350                                                                              1   73       16 14 -15      -14 -7.0                             MnO 0.01                                                                      CoO 0.5                                                         750  2   0.5           1350                                                                              1   104      18 16 -12      -11 -4.5                             MnO 0.5                                                                       CoO 0.5                                                         750  2   0.5           1350                                                                              1   125      17 15 -15      -15 -6.5                             MnO 5.0                                                                       CoO 0.05                                                        750  2   0.5           1350                                                                              1   93       17 15 -14      -15 -6.7                             MnO 0.5                                                                       CoO 1.0                                                         750  2   0.5           1350                                                                              1   106      19 17 -14      -14 -6.8                             MnO 0.5                                                                       CoO 9.5                                                         750  2   0.5           1300                                                                              2   130      18 16 -15      -15 -6.9                             MnO 0.5                                                                       CoO 0.5                                                         500  10  0.5           1350                                                                              1   110      17 15 -15      -12 -5.8                             MnO 0.5                                                                       CoO 0.5                                                         700  2   0.5           1350                                                                              1   105      17 16 -12      -11 -4.6                             MnO 0.5                                                                       CoO 0.5                                                         800  2   0.5           1350                                                                              1   106      17 16 -12      -11 -4.5                             MnO 0.5                                                                       CoO 0.5                                                         1000 1   0.5           1350                                                                              1   115      16 14 -14      -12 -5.9                             MnO 0.5                                                                       CoO 0.5                                                         700  2   0.5           1300                                                                              2   58       26 17 -12      -12 -4.6                             BaO 0.5                                                                       CoO 0.5                                                         700  2   0.5           1300                                                                              2   102      23 14 -15      -14 -6.3                             BaO 9.5                                                                       CoO 9.5                                                         800  1   0.5           1300                                                                              2   92       22 13 -15      -15 -6.5                             BaO 0.5                                                                       CoO 0.5                                                         500  5   0.5           1300                                                                              2   61       24 15 -13      -13 -5.2                             BaO 0.5                                                                       CoO 0.5                                                         800  2   0.5           1300                                                                              2   59       25 16 -12      -12 -4.7                             BaO 0.5                                                                       CoO 0.5                                                         1000 2   0.5           1300                                                                              2   59       25 16 -15      -13 -5.1                             BaO 0.5                                                                       CoO 0.5                                                         700  2   0.5           1350                                                                              1   180      30 19 -11      -12 -3.4                             Sb.sub.2 O.sub.3                                                                  0.5                                                                       CoO 0.5                                                         700  2   0.5           1350                                                                              1   350      26 17 -15      -15 -5.5                             Sb.sub.2 O.sub.3                                                                  9.5                                                                       CoO 9.5                                                         700  2   0.5           1350                                                                              1   250      27 18 -14      -15 -5.2                             Sb.sub.2 O.sub.3                                                                  0.5                                                                       CoO 0.5                                                         500  10  0.5           1350                                                                              1   190      29 19 -12      -13 -4.2                             Sb.sub.2 O.sub.3                                                                  0.5                                                                       CoO 0.5                                                         800  2   0.5           1350                                                                              1   180      30 19 -11      -12 -3.5                             Sb.sub.2 O.sub.3                                                                  0.5                                                                       CoO 0.5                                                         1000 1   0.5           1350                                                                              1   185      30 18 -12      -12 -4.5                             Sb.sub.2 O.sub.3                                                                  0.5                                                                       MnO 0.005                                                       700  2   0.01          1350                                                                              1   605      8  6  -15      -13 -5.5                             SrO 0.005                                                                     MnO 0.05                                                        700  2   0.01          1350                                                                              1   600      9  7  -15      -15 -6.2                             SrO 9.95                                                                      MnO 0.005                                                       700  2   10.0          1350                                                                              1   580      8  6  -15      -14 -6.3                             SrO 0.005                                                                     MnO 0.05                                                        700  2   10.0          1350                                                                              1   560      8  6  -14      -15 -6.5                             SrO 9.95                                                                      MnO 9.95                                                        700  2   0.05          1350                                                                              1   700      8  6  -14      -15 -5.5                             SrO 0.05                                                                      MnO 5.0                                                         700  2   0.05          1350                                                                              1   450      9  7  -15      -15 -5.3                             SrO 5.0                                                                       MnO 9.95                                                        700  2   10.0          1350                                                                              1   480      8  6  -14      -15 -5.2                             SrO 0.05                                                                      MnO 5.0                                                         700  2   10.0          1350                                                                              1   470      9  8  -15      -14 -6.1                             SrO 5.0                                                                       MnO 0.1                                                         700  2   0.1           1350                                                                              1   200      10 8  -14      -                                                                                 -5.8                             SrO 0.1                                                                       MnO 0.1                                                         700  2   0.1           1350                                                                              1   200      11 7  -15      -15 -5.9                             SrO 3.0                                                                       MnO 0.1                                                         700  2   3.0           1350                                                                              1   200      11 9  -15      -14 -5.8                             SrO 0.1                                                                       MnO 0.1                                                         700  2   3.0           1350                                                                              1   190      11 9  -16      -15 -5.7                             SrO 3.0                                                                       MnO 3.0                                                         700  2   0.1           1350                                                                              1   210      11 9  -15      -15 -5.5                             SrO 0.1                                                                       MnO 3.0                                                         700  2   0.1           1350                                                                              1   205      11 9  -16      -15 -5.9                             SrO 3.0                                                                       MnO 9.9                                                         700  2   3.0           1350                                                                              2   210      11 9  -16      -14 -5.4                             SrO 0.1                                                                       MnO 3.0                                                         700  2   3.0           1350                                                                              2   205      11 9  -15      -15 -5.5                             SrO 3.0                                                                       MnO 0.5                                                         700  2   0.5           1350                                                                              1   70       25 19 -11      -11 -3.9                             SrO 0.5                                                                       MnO 0.5                                                         500  10  0.5           1350                                                                              1   75       25 17 -12      -13 -5.0                             SrO 0.5                                                                       MnO 0.5                                                         800  2   0.5           1350                                                                              1   72       25 19 -11      -10 -3.8                             SrO 0.5                                                                       MnO 0.5                                                         1000 1   0.5           1350                                                                              1   80       25 17 -13      -14 -5.0                             SrO 0.5                                                                       CoO 0.5                                                         1000 1   0.5           1350                                                                              1   15       28 18 -17      -15 -5.8                             SrO 0.5                                                                       CoO 0.5                                                         800  2   0.5           1350                                                                              1   13       28 19 -13      -12 -3.5                             SrO 0.5                                                                       CoO 0.5                                                         700  2   0.5           1350                                                                              1   14       28 19 -13      -13 -3.6                             SrO 0.5                                                                       CoO 0.5                                                         500  10  0.5           1350                                                                              1   15       27 17 -18      -14 -5.7                             SrO 0.5                                                                       MnO 0.5                                                         500  10  0.5           1350                                                                              1   70       26 17 -17      -16 -5.8                             BaO 0.5                                                                       MnO 0.5                                                         700  2   0.5           1350                                                                              1   68       26 19 -14      -12 -4.1                             BaO 0.5                                                                       MnO 0.5                                                         800  2   0.5           1350                                                                              1   65       26 19 -13      -12 -4.0                             BaO 0.5                                                                       MnO 0.5                                                         1000 1   0.5           1350                                                                              1   71       27 16 -16      -15 -6.0                             BaO 0.5                                                                       MnO 0.5                                                         500  10  0.5           1350                                                                              1   155      33 17 -15      -14 -5.9                             Sb.sub.2 O.sub.3                                                                  0.5                                                                       MnO 0.5                                                         700  2   0.5           1350                                                                              1   150      33 19 -11      -11 -3.8                             Sb.sub.2 O.sub.3                                                                  0.5                                                                       MnO 0.5                                                         800  2   0.5           1350                                                                              1   150      33 19 -12      -11 -3.5                             Sb.sub.2 O.sub.3                                                                  0.5                                                                       MnO 0.5                                                         1000 1   0.5           1350                                                                              1   160      33 17 -16      -15 -6.1                             Sb.sub.2 O.sub.3                                                                  0.5                                                                       BaO 0.005                                                       700  2   0.01          1350                                                                              1   380      11 9  -17      -16 -6.0                             SrO 0.005                                                                     BaO 0.05                                                        700  2   0.01          1350                                                                              2   390      11 9  -17      -16 -6.0                             SrO 9.95                                                                      BaO 0.005                                                       700  2   10.0          1350                                                                              2   350      11 9  -16      -15 -6.1                             SrO 0.005                                                                     BaO 0.05                                                        700  2   10.0          1350                                                                              2   400      10 9  -15      -16 -6.5                             SrO 9.95                                                                      BaO 9.95                                                        700  2   0.01          1350                                                                              1   380      11 9  -17      -16 -6.3                             SrO 0.05                                                                      BaO 5.0                                                         700  2   0.01          1350                                                                              1   375      11 9  -16      -15 -6.3                             SrO 5.0                                                                       BaO 9.95                                                        700  2   10.0          1350                                                                              2   35       12 10 -17      -16 -6.5                             SrO 0.05                                                                      BaO 5.0                                                         700  2   10.0          1350                                                                              2   30       11 9  -17      -15 -6.4                             SrO 5.0                                                                       BaO 0.5                                                         500  10  0.5           1350                                                                              1   23       30 16 -13      -12 -4.5                             SrO 0.5                                                                       BaO 0.5                                                         700  2   0.5           1350                                                                              1   21       31 19 -12      -10 -3.0                             SrO 0.5                                                                       BaO 0.5                                                         800  2   0.5           1350                                                                              1   21       31 18 -12      -10 -3.2                             SrO 0.5                                                                       BaO 0.5                                                         1000 1   0.5           1350                                                                              1   25       30 16 -13      -13 -4.4                             SrO 0.5                                                                       BaO 0.5                                                         500  10  0.5           1350                                                                              1   80       27 16 -13      -13 -4.8                             Sb.sub.2 O.sub.3                                                                  0.5                                                                       BaO 0.5                                                         700  2   0.5           1350                                                                              1   73       26 19 -11      -11 -3.8                             Sb.sub.2 O.sub.3                                                                  0.5                                                                       BaO 0.5                                                         800  2   0.5           1350                                                                              1   72       26 19 -11      -11 -3.9                             Sb.sub.2 O.sub.3                                                                  0.5                                                                       BaO 0.5                                                         1000 1   0.5           1350                                                                              1   85       28 17 -13      -12 -4.9                             Sb.sub.2 O.sub.3                                                                  0.5                                                                       SrO 0.5                                                         500  10  0.5           1350                                                                              1   65       24 15 -14      -13 -4.6                             Sb.sub.2 O.sub.3                                                                  0.5                                                                       SrO 0.5                                                         700  2   0.5           1350                                                                              1   60       24 15 -11      -10 -3.1                             Sb.sub.2 O.sub.3                                                                  0.5                                                                       SrO 0.5                                                         800  2   0.5           1350                                                                              1   62       24 16 -11      -10 -3.2                             Sb.sub.2 O.sub.3                                                                  0.5                                                                       SrO 0.5                                                         1000 1   0.5           1350                                                                              1   71       25 14 -13      -13 -4.8                             Sb.sub.2 O.sub.3                                                                  0.5                                                         500  10  0.5  SrO 0.5  1350                                                                              1   18       25 16 -15      -15 -4.6                             PbO 0.5                                                                       SrO 0.5                                                         700  2   0.5           1350                                                                              1   13       25 18 -12      -12 -3.5                             PbO 0.5                                                                       SrO 0.5                                                         800  2   0.5           1350                                                                              1   13       25 18 -12      -12 -3.4                             PbO 0.5                                                                       SrO 0.5                                                         1000 1   0.5           1350                                                                              1   17       26 16 -14      -15 -4.5                             PbO 0.5                                                                       BaO 0.5                                                         500  10  0.5           1350                                                                              1   71       20 13 -14      -13 -4.7                             PbO 0.5                                                                       BaO 0.5                                                         700  2   0.5           1350                                                                              1   69       21 14 -12      -11 -3.3                             PbO 0.5                                                                       BaO 0.5                                                         800  2   0.5           1350                                                                              1   69       21 14 -12      -10 -3.7                             PbO 0.5                                                                       BaO 0.5                                                         1000 1   0.5           1350                                                                              1   75       22 13 -13      -14 -4.8                             PbO 0.5                                                                       Sb.sub.2 O.sub.3                                                                  0.5                                                         500  10  0.5           1350                                                                              1   130      20 11 -16      -15 -5.0                             PbO 0.5                                                                       Sb.sub.2 O.sub.3                                                                  0.5                                                         700  2   0.5           1350                                                                              1   120      21 13 -13      -12 -3.8                             PbO 0.5                                                                       Sb.sub.2 O.sub.3                                                                  0.5                                                         800  2   0.5           1350                                                                              1   118      21 13 -13      -11 -3.1                             PbO 0.5                                                                       Sb.sub.2 O.sub.3                                                                  0.5                                                         1000 1   0.5           1350                                                                              1   125      20 10 -15      -14 -5.0                             Pb0 0.5                                                                       MnO 0.5                                                         500  10  0.5           1350                                                                              1   92       22 13 -15      -16 -4.5                             PbO 0.5                                                                       MnO 0.5                                                         700  2   0.5           1350                                                                              1   80       22 15 -12      -13 -3.3                             PbO 0.5                                                                       MnO 0.5                                                         800  2   0.5           1350                                                                              1   80       22 15 -13      -12 -3.1                             PbO 0.5                                                                       MnO 0.5                                                         1000 1   0.5           1350                                                                              1   90       23 12 -16      -14 -5.0                             PbO 0.5                                                                       CoO 0.5                                                         500  10  0.5           1350                                                                              1   75       20 11 -14      -15 -4.9                             PbO 0.5                                                                       CoO 0.5                                                         700  2   0.5           1350                                                                              1   70       21 14 -11      -12 -3.5                             PbO 0.5                                                                       CoO 0.5                                                         800  2   0.5           1350                                                                              1   72       21 14 -11      -11 -3.4                             PbO 0.5                                                                       CoO 0.5                                                         1000 1   0.5           1350                                                                              1   80       21 12 -15      -14 -5.0                             PbO 0.5                                                         __________________________________________________________________________

EXAMPLE 4

Zinc oxide and additives of Table 4 were fabricated intovoltage-dependent resistors by the same process as that of Example 2,except the sintering condition was 1350°C for 1 hour. The electricalcharacteristics of the resulting resistors are shown in Table 4. Thechange rates of C- and n-values after impulse test carried out by thesame method as that of Example 3 are shown in Table 4. It will be easilyunderstood that the heat-treating of zinc oxide powder results in thehigher n-value, smaller change rate and low C-value, compared with theabove mentioned U.S. Patent applications. The preferred results can beobtained when the heat-treating temperature of the zinc oxide powder isbetween 700°C and 800°C.

                                      Table 4                                     __________________________________________________________________________    Heat-treating                                                                          Additives             Electrical characteristics                                                                  Change Rate after Impulse        of zinc oxide                                                                          (mole %)              of Resultant Resistor                                                                       Test (%)                         powder                                                                        __________________________________________________________________________                          other    C (at a given                                  Temp.                                                                              Time                                                                              Bi.sub.2 O.sub.3                                                                   CoO MnO additives                                                                              current of                                                                            n.sub.1                                                                          n.sub.2                                                                          ΔC (at a given             (°C)                                                                        (hrs.)                    1mA) (V)      current of                                                                              Δn.sub.1                                                                    Δn.sub.2     __________________________________________________________________________    700  2   0.01 0.1 0.1 Sb.sub.2 O.sub.3                                                                    0.01                                                                             45      50 20 -9.4      -10 -5.3               700  2   0.01 0.1 0.1 Sb.sub.2 O.sub.3                                                                    8.0                                                                              56      51 21 -9.3      -8.4                                                                              -4.8               700  2   0.01 3.0 0.1 Sb.sub.2 O.sub.3                                                                    0.01                                                                             42      51 20 -8.7      -9.4                                                                              -4.7               700  2   0.01 0.1 3.0 Sb.sub.2 O.sub.3                                                                    0.01                                                                             50      52 22 -9.5      -10 -4.8               700  2   0.01 3.0 3.0 Sb.sub.2 O.sub.3                                                                    0.01                                                                             58      50 23 -8.7      -                                                                                 -4.9               700  2   0.01 0.1 3.0 Sb.sub.2 O.sub.3                                                                    8.0                                                                              52      52 25 -8.7      -9.8                                                                              -4.6               700  2   0.01 3.0 0.1 Sb.sub.2 O.sub.3                                                                    8.0                                                                              51      51 24 -9.3      -8.3                                                                              -4.6               700  2   10.0 3.0 0.1 Sb.sub.2 O.sub.3                                                                    0.01                                                                             35      50 24 -9.5      -8.2                                                                              -4.9               700  2   10.0 0.1 3.0 Sb.sub.2 O.sub.3                                                                    0.01                                                                             41      52 25 -9.0      -9.6                                                                              -4.9               700  2   10.0 0.1 0.1 Sb.sub.2 O.sub.3 8.0                                                                48 52      25 -8.3                                                                             -9.7      -5.1                   700  2   0.01 3.0 3.0 Sb.sub.2 O.sub.3                                                                    8.0                                                                              53      52 25 -9.6      -9.9                                                                              -5.2               700  2   10.0 0.1 3.0 Sb.sub.2 O.sub.3                                                                    8.0                                                                              55      50 23 -10       -8.4                                                                              -4.8               700  2   10.0 3.0 0.1 Sb.sub.2 O.sub.3                                                                    8.0                                                                              60      51 24 -10       -9.8                                                                              -4.5               700  2   10.0 3.0 3.0 Sb.sub.2 0.sub.3                                                                    0.01                                                                             60      53 24 -10       -10 -4.1               700  2   10.0 3.0 3.0 Sb.sub.2 O.sub.3                                                                    8.0                                                                              53      53 23 -10       -9.6                                                                              -3.8               500  10  0.5  0.5 0.5 Sb.sub. 2 O.sub.3                                                                   1.0                                                                              70      59 24 -7.2      -6.4                                                                              -3.7               700  2   0.5  0.5 0.5 Sb.sub.2 O.sub.3                                                                    1.0                                                                              45      60 26 -6.2      -5.3                                                                              -3.8               800  2   0.5  0.5 0.5 Sb.sub.2 O.sub.3                                                                    1.0                                                                              43      59 25 -6.4      -5.2                                                                              -3.9               1000 1   0.5  0.5 0.5 Sb.sub.2 O.sub.3                                                                    1.0                                                                              65      60 24 -7.3      -6.0                                                                              -4.1               700  2   0.01 0.1 0.1 SnO.sub.2                                                                           0.1                                                                              75      48 20 -10       -10 -4.2               700  2   10.0 3.0 3.0 SnO.sub.2                                                                           5.0                                                                              73      48 21 -9.5      -9.9                                                                              -4.3               500  10  0.5  0.5 0.5 SnO.sub.2                                                                           0.5                                                                              62      50 22 -7.8      -8.4                                                                              -4.3               700  2   0.5  0.5 0.5 SnO.sub.2                                                                           0.5                                                                              50      60 23 -5.2      -5.0                                                                              -3.7               800  2   0.5  0.5 0.5 SnO.sub.2                                                                           0.5                                                                              48      60 24 -5.3      -5.2                                                                              -3.0               1000 1   0.5  0.5 0.5 SnO.sub.2                                                                           0.5                                                                              58      52 21 -8.2      -7.3                                                                              -4.5               1000 10  0.5  0.5 0.5 SiO.sub.2                                                                           0.5                                                                              81      40 24 -8.7      -8.1                                                                              -3.9               700  2   0.01 0.1 0.1 SiO.sub. 2                                                                          0.01                                                                             78      41 20 - 8.4     -9.5                                                                              -4.4               700  2   10.0 3.0 3.0 SiO.sub.2                                                                           10.0                                                                             95      40 21 -8.0      -9.2                                                                              -4.2               500  10  0.5  0.5 0.5 SiO.sub.2                                                                           0.5                                                                              80      42 21 -7.4      -8.2                                                                              -3.7               700  2   0.5  0.5 0.5 SiO.sub.2                                                                           0.5                                                                              60      51 25 -5.0      -5.9                                                                              -2.2               800  2   0.5  0.5 0.5 SiO.sub.2                                                                           0.5                                                                              58      50 26 -5.2      -5.6                                                                              -2.1               1000 1   0.5  0.5 0.5 SiO.sub.2                                                                           0.5                                                                              70      45 22 -9.0      -8.2                                                                              -3.9                                     Sb.sub.2 O.sub.3                                                                    0.01                                              700  2   0.5  0.5 0.5          95      70 20 -7.6      -8.1                                                                              -5.3                                     SnO.sub.2                                                                           0.1                                                                     Sb.sub.2 O.sub.3                                                                    0.1                                               700  2   0.5  0.5 0.5          80      69 21 -7.3      -8.0                                                                              -3.1                                     SnO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    0.5                                               700  2   0.5  0.5 0.5          70      71 20 -7.9      -7.7                                                                              -3.2                                     SnO.sub.2                                                                           5.0                                                                     Sb.sub.2 O.sub.3                                                                    0.01                                              700  2   0.5  0.5 0.5          90      70 22 -8.3      -7.3                                                                              -3.2                                     SnO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    8.0                                               700  2   0.5  0.5 0.5          72      70 20 -8.2      -7.4                                                                              -3.3                                     SnO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               500  10  0.5  0.5 0.5          60      71 23 -7.6      -8.0                                                                              -2.5                                     SnO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               700  2   0.5  0.5 0.5          55      80 26 -5.2      -5.1                                                                              -1.6                                     SnO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               800  2   0.5  0.5 0.5          54      80 27 -5.4      -5.2                                                                              -1.8                                     SnO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               1000 1   0.5  0.5 0.5          65      74 24 -7.6      -6.8                                                                              -2.3                                     SnO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               500  10  0.5  0.5 0.5          75      70 21 -7.3      -8.2                                                                              -2.7                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               700  2   0.5  0.5 0.5          50      79 26 -6.0      -5.7                                                                              -1.5                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               800  2   0.5  0.5 0.5          48      78 26 -6.1      -5.3                                                                              -1.7                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               1000 5   0.5  0.5 0.5          70      71 23 -7.8      -7.8                                                                              -2.8                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               500  10  0.5  0.5 0.5          73      71 22 -8.0      -8.6                                                                              -3.0                                     SiO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               700  2   0.5  0.5 0.5          48      80 26 -5.0      -5.9                                                                              -1.7                                     SiO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               800  2   0.5  0.5 0.5          46      79 25 -5.4      -5.4                                                                              -1.7                                     SiO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               1000 1   0.5  0.5 0.5          68      72 22 -7.9      -8.3                                                                              -2.9                                     SiO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               500  10  0.5  0.5 0.5          68      70 22 -8.0      -7.8                                                                              -3.0                                     NiO   0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               700  2   0.5  0.5 0.5          43      79 27 -5.1      -5.2                                                                              -1.5                                     NiO   0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               800  2   0.50 0.5 0.5          41      77 28 -5.0      -5.0                                                                              -1.4                                     NiO   0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               1000 1   0.5  0.5 0.5          64      70 23 -7.6      -8.3                                                                              -2.9                                     NiO   0.5                                                                     Cr.sub.2 O.sub.3                                                                    0.5                                               500  10  0.5  0.5 0.5          95      75 25 -8.8      -8.4                                                                              -5.1                                     SiO.sub.2                                                                           0.5                                                                     Cr.sub.2 O.sub.3                                                                    0.5                                               700  2   0.5  0.5 0.5          72      80 29 -5.1      -5.4                                                                              -1.4                                     SiO   0.5                                                                     Cr.sub.2 O.sub.3                                                                    0.5                                               800  2   0.5  0.5 0.5          70      81 27 -5.1      -5.1                                                                              -1.3                                     SiO.sub.2                                                                           0.5                                                                     Cr.sub.2 O.sub.3                                                                    0.5                                               1000 1   0.5  0.5 0.5          89      74 24 -6.6      -8.5                                                                              -3.0                                     SiO.sub.2                                                                           0.5                                                                     SnO.sub.2                                                                           0.5                                               500  10  0.5  0.5 0.5          70      72 25 -6.6      -6.5                                                                              -2.9                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     SnO.sub.2                                                                           0.5                                               700  2   0.5  0.5 0.5          65      82 30 -;5.0     -5.2                                                                              -1.8                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     SnO.sub.2                                                                           0.5                                               800  2   0.5  0.5 0.5          64      81 30 -5.1      -4.7                                                                              -1.7                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     SiO.sub.2                                                                           0.5                                               1000 1   0.5  0.5 0.5          75      73 20 -6.5      -6.0                                                                              -3.1                                     NiO   0.5                                                                     SiO.sub.2                                                                           0.5                                               500  10  0.5  0.5 0.5          70      70 20 -6.3      -6.5                                                                              -2.9                                     NiO   0.5                                                                     SiO.sub.2                                                                           0.5                                               700  2   0.5  0.5 0.5          63      75 27 -5.0      -5.1                                                                              -1.4                                     NiO   0.5                                                                     SiO.sub.2                                                                           0.5                                               800  2   0.5  0.5 0.5          60      74 28 -4.9      -4.8                                                                              -1.7                                     NiO   0.5                                                                     SnO.sub.2                                                                           0.5                                               1000 1   0.5  0.5 0.5          72      69 20 -6.9      -7.0                                                                              -2.9                                     SiO.sub.2                                                                           0.5                                                                     SnO.sub.2                                                                           0.5                                               500  10  0.5  0.5 0.5          95      75 25 -7.3      -8.1                                                                              -2.7                                     SiO.sub.2                                                                           0.5                                                                     SnO.sub.2                                                                           0.5                                               700  2   0.5  0.5 0.5          80      80 29 -5.1      -5.2                                                                              -1.4                                     SiO.sub.2                                                                           0.5                                                                     SnO.sub.2                                                                           0.5                                               800  2   0.5  0.5 0.5          81      81 29 -5.2      -5.0                                                                              -1.3                                     SiO.sub.2                                                                           0.5                                                                     SnO.sub.2                                                                           0.5                                               1000 1   0.5  0.5 0.5          100     70 24 -6.8      -7.5                                                                              -2.3                                     NiO   0.5                                                                     SnO.sub.2                                                                           0.5                                               500  10  0.5  0.5 0.5          60      50 25 -6.7      -7.4                                                                              -2.4                                     NiO   0.5                                                                     SnO.sub.2                                                                           0.5                                               700  2   0.5  0.5 0.5          32      62 30 -5.5      -5.8                                                                              -1.7                                     NiO   0.5                                                                     SnO.sub.2                                                                           0.5                                               800  2   0.5  0.5 0.5          30      60 30 -7.1      -5.5                                                                              -1.6                                     NiO   0.5                                                                     SnO.sub.2                                                                           0.5                                               1000 1   0.5  0.5 0.5          70      49 24 -6.9      -8.0                                                                              -2.4                                     NiO   0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               500  10  0.5  0.5 0.5 SnO.sub.2                                                                           0.5                                                                              120     71 25 -4.8      -2.1                                                                              -2.0                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               700  2   0.5  0.5 0.5 SnO.sub.2                                                                           0.5                                                                              105     80 31 -2.3      -0.6                                                                              -0.8                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               800  2   0.5  0.5 0.5 SnO.sub.2                                                                           0.5                                                                              100     80 31 -2.2      -0.7                                                                              -0.7                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               1000 1   0.5  0.5 0.5 SnO   0.5                                                                              140     70 27 - 4.3     -2.1                                                                              -2.0                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               500  10  0.5  0.5 0.5 SnO.sub.2                                                                           0.5                                                                              125     72 25 -4.5      -2.0                                                                              -1.7                                     SiO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               700  2   0.5  0.5 0.5 SnO.sub.2                                                                           0.5                                                                              100     79 28 -2.0      -0.8                                                                              -0.6                                     SiO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               800  2   0.5  0.5 0.5 SnO.sub.2                                                                           0.5                                                                              95      80 28 -2.3      -0.6                                                                              -0.7                                     SiO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               1000 1   0.5  0.5 0.5 SnO.sub.2                                                                           0.5                                                                              130     73 24 -4.0      -2.1                                                                              -1.5                                     SiO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               500  10  0.5  0.5 0.5 SnO.sub.2                                                                           0.5                                                                              210     70 25 -3.9      -2.4                                                                              -1.6                                     NiO   0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               700  2   0.5  0.5 0.5 SnO.sub.2                                                                           0.5                                                                              170     82 32 -2.7      -1.1                                                                              -0.8                                     NiO   0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               800  2   0.5  0.5 0.5 SnO.sub.2                                                                           0.5                                                                              165     81 30 -2.3      -1.2                                                                              -1.1                                     NiO   0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               1000 1   0.5  0.5 0.5 SnO.sub.2                                                                           0.5                                                                              250     65 24 -4.0      -2.3                                                                              -1.6                                     NiO   0.5                                                                     SnO.sub.2                                                                           0.5                                               500  10  0.5  0.5 0.5 SiO.sub.2                                                                           0.5                                                                              230     69 24 -4.2      -3.1                                                                              -2.1                                     NiO   0.5                                                                     SnO.sub.2                                                                           0.5                                               700  2   0.5  0.5 0.5 SiO.sub.2                                                                           0.5                                                                              140     75 30 -2.5      -1.4                                                                              -0.7                                     NiO   0.5                                                                     SnO.sub.2                                                                           0.5                                               800  2   0.5  0.5 0.5 SiO.sub.2                                                                           0.5                                                                              160     76 31 -2.3      -1.6                                                                              -0.8                                     NiO   0.5                                                                     SnO.sub.2                                                                           0.5                                               1000 1   0.5  0.5 0.5 SiO.sub.2                                                                           0.5                                                                              200     67 25 -4.3      -3.0                                                                              -2.1                                     NiO   0.5                                                                     SiO.sub.2                                                                           0.5                                               500  10  0.5  0.5 0.5 NiO   0.5                                                                              250     70 25 -4.1      -0.8                                                                              -1.8                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     SiO.sub.2                                                                           0.5                                               700  2   0.5  0.5 0.5 NiO   0.5                                                                              230     78 30 -2.0      -1.7                                                                              -1.0                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     SiO.sub.2                                                                           0.5                                               800  2   0.5  0.5 0.5 NiO   0.5                                                                              220     78 31 -2.3      -1.4                                                                              -0.8                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     SiO.sub.2                                                                           0.5                                               1000 1   0.5  0.5 0.5 NiO   0.5                                                                              260     71 24 -4.3      -0.9                                                                              -2.1                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               500  10  0.5  0.5 0.5 NiO   0.5                                                                              180     72 22 -3.2      -3.1                                                                              -2.5                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               700  2   0.5  0.5 0.5 NiO   0.5                                                                              150     80 28 -0.9      -1.3                                                                              -0.2                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               800  2   0.5  0.5 0.5 NiO   0.5                                                                              140     81 30 -2.6      -0.8                                                                              -0.9                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               1000 1   0.5  0.5 0.5 NiO   0.5                                                                              190     73 21 -4.1      -2.3                                                                              -1.5                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     SnO.sub.2                                                                           0.5                                               500  10  0.5  0.5 0.5 NiO   0.5                                                                              70      70 25 -4.4      -2.5                                                                              -1.7                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     SnO.sub.2                                                                           0.5                                               700  2   0.5  0.5 0.5 NiO   0.5                                                                              50      81 31 -2.6      -1.3                                                                              -0.8                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     SnO.sub.2                                                                           0.5                                               800  2   0.5  0.5 0.5 NiO   0.5                                                                              48      80 32 -2.5      -1.1                                                                              -0.7                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     SnO.sub.2                                                                           0.5                                               1000 1   0.5  0.5 0.5 NiO   0.5                                                                              70      73 26 -4.2      -2.5                                                                              -1.8                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               500  10  0.5  0.5 0.5 NiO   0.5                                                                              105     65 25 -4.4      -3.3                                                                              -1.9                                     SiO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               700  2   0.5  0.5 0.5 NiO   0.5                                                                              72      79 31 -2.4      -1.3                                                                              -0.9                                     SiO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               800  2   0.5  0.5 0.5 NiO   0.5                                                                              70      75 32 -2.2      -1.5                                                                              -1.0                                     SiO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               1000 1   0.5  0.5 0.5 NiO   0.5                                                                              95      62 26 -4.6      -3.1                                                                              -2.2                                     SiO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               500  10  0.5  0.5 0.5 SiO.sub.2                                                                           0.5                                                                              130     70 25 -4.6      -3.8                                                                              -2.1                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               700  2   0.5  0.5 0.5 SiO.sub.2 0.5                                                                       100                                                                              79      32 -2.3                                                                             -0.9      -1.0                                         Cr.sub.2 O.sub.3                                                                    0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               800  2   0.5  0.5 0.5 SiO.sub.2                                                                           0.5                                                                              95      78 33 -2.1      -1.0                                                                              -0.8                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               1000 1   0.5  0.5 0.5 SiO.sub.2                                                                           0.5                                                                              140     69 26 -4.7      -2.9                                                                              -2.3                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     SnO.sub.2                                                                           0.5                                               500  10  0.5  0.5 0.5 NiO   0.5                                                                              80      70 27 -3.5      -3.8                                                                              -2.5                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     SnO.sub.2                                                                           0.5                                               700  2   0.5  0.5 0.5 NiO   0.5                                                                              62      78 32 -0.9      -1.1                                                                              -0.4                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     SnO.sub.2                                                                           0.5                                               800  2   0.5  0.5 0.5 NiO   0.5                                                                              65      79 33 -2.2      -0.4                                                                              -0.9                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     SnO.sub.2                                                                           0.5                                               1000 1   0.5  0.5 0.5 NiO   0.5                                                                              83      72 28 -4.3      -1.1                                                                              -1.4                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                                                     SnO.sub.2                                                                           0.5                                               500  10  0.5  0.5 0.5          75      80 31 -2.1      +0.1                                                                              +0.2                                     NiO   0.5                                                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                                                     SnO.sub.2                                                                           0.5                                               700  2   0.5  0.5 0.5          60      85 35 -1.5      +1.8                                                                              +2.0                                     NiO   0.5                                                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                                                     SnO.sub.2                                                                           0.5                                               800  2   0.5  0.5 0.5          58      86 36 -1.3      +1.7                                                                              +2.0                                     NiO   0.5                                                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                               SnO.sub.2                                                                          0.5                                                                      1000 1   0.5  0.5 0.5          80      79 30 -2.1      +0.2                                                                              +0.5                                     NiO   0.5                                                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                                                     NiO   0.5                                               500  10  0.5  0.5 0.5          80      80 30 -1.0      +0.5                                                                              +0.2                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     SiO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                                                     NiO   0.5                                               700  2   0.5  0.5 0.5          62      87 37 -0.5      +1.3                                                                              +1.3                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     SiO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                                                     NiO   0.5                                               800  2   0.5  0.5 0.5          60      88 38 -0.1      +1.5                                                                              +1.4                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     SiO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                                                     NiO   0.5                                               1000 1   0.5  0.5 0.5          85      84 31 -1.3      +0.3                                                                              +0.5                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     SiO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                                                     SnO.sub.2                                                                           0.5                                               500  10  0.5  0.5 0.5          105     80 29 -2.5      +0.4                                                                              +0.4                                     NiO   0.5                                                                     SiO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                                                     SnO.sub.2                                                                           0.5                                               700  2   0.5  0.5 0.5          62      89 40 -0.9      +1.3                                                                              +1.4                                     NiO   0.5                                                                     SiO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                                                     SnO.sub.2                                                                           0.5                                               800  2   0.5  0.5 0.5          60      90 41 -0.7      +1.4                                                                              +1.8                                     NiO   0.5                                                                     SiO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                                                     SnO.sub.2                                                                           0.5                                               1000 1   0.5  0.5 0.5          95      81 33 -1.9      +0.6                                                                              +0.2                                     NiO   0.5                                                                     SiO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                                                     SnO.sub.2                                                                           0.5                                               500  10  0.5  0.5 0.5          100     80 30 -1.9      +0.9                                                                              +0.3                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     SiO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                                                     SnO.sub.2                                                                           0.5                                               700  2   0.5  0.5 0.5          60      88 38 -1.0      +3.8                                                                              +1.8                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     SiO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                                                     SnO.sub.2                                                                           0.5                                               800  2   0.5  0.5 0.5          70      90 39 -1.1      +3.7                                                                              +1.7                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     SiO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                                                     SnO.sub.2                                                                           0.5                                               1000 1   0.5  0.5 0.5          95      81 32 -1.8      +1.0                                                                              +0.5                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     SiO.sub.2                                                                           0.5                                                                     SnO.sub.2                                                                           0.5                                                                     NiO   0.5                                               500  10  0.5  0.5 0.5          50      70 30 -1.6      +2.5                                                                              +0.1                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     SiO.sub.2                                                                           0.5                                                                     SnO.sub.2                                                                           0.5                                                                     NiO   0.5                                               700  2   0.5  0.5 0.5          33      78 35 -1.0      +4.3                                                                              +1.9                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     SiO.sub.2                                                                           0.5                                                                     SnO.sub.2                                                                           0.5                                                                     NiO   0.5                                               800  2   0.5  0.5 0.5          26      80 36 -0.9      +4.1                                                                              +1.7                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     SiO.sub.2                                                                           0.5                                                                     SnO.sub.2                                                                           0.5                                                                     NiO   0.5                                               1000 1   0.5  .5  0.5          60      72 31 -1.9      +0.3                                                                              +0.4                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     SiO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                                                     SnO.sub.2                                                                           0.5                                               500  10  0.5  0.5 0.5 NiO   0.5                                                                              70      80 32 -0.7      +2.6                                                                              +2.3                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     SiO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                                                     SnO.sub.2                                                                           0.5                                               700  2   0.5  0.5 0.5 NiO   0.5                                                                              62      89 40 -0.6      +2.9                                                                              +3.4                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     SiO.sub.2                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                                                     SnO.sub.2                                                                           0.5                                               800  2   0.5  0.5 0.5 NiO   0.5                                                                              60      90 41 -0.2      +7.2                                                                              +6.2                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     SiO.sub.3                                                                           0.5                                                                     Sb.sub.2 O.sub.3                                                                    1.0                                                                     SnO.sub.2                                                                           0.5                                               1000 1   0.5  0.5 0.5 NiO   0.5                                                                              69      81 33 -0.1      +2.0                                                                              +1.0                                     Cr.sub.2 O.sub.3                                                                    0.5                                                                     SiO.sub.2                                                                           0.5                                               __________________________________________________________________________

EXAMPLE 5

Zinc oxide and additives of Table 5 were fabricated intovoltage-dependent resistors by the same process as that of Example 4.The electrical characteristics of the resultant resistors are shown inTable 5. It will be easily understood that the heat-treating of zincoxide powder results in the higher n-value, smaller change rate andlower C-value without reducing the n-value. The preferred results can beobtained when the heat-treating temperature of the zinc oxide powder isbetween 700°C and 800°C.

                                      Table 5                                     __________________________________________________________________________    Heat-treating                                                                          Additives             Electrical characteristics                                                                  Change Rate after Impulse        of zinc oxide                                                                          (mole %)              of Resultant resistor                                                                       Test (%)                         powder                                                                        __________________________________________________________________________                          other     C(at a given                                  Temp.                                                                              Time                                                                              Bi.sub.2 O.sub.3                                                                   CoO MnO additives                                                                              Current of 1mA)                                                                         n.sub.1                                                                         n.sub.2                                                                         Δ C(at a                                                                          Δn.sub.1                                                                    Δn.sub.2                                                                .                  (°C)                                                                        (hrs.)                    (V)           current of                       __________________________________________________________________________                                                 1mA)                             700  2   0.01 0.1 0.1 TiO.sub.2                                                                          0.1 15        45                                                                              20                                                                              -9.2      -10 -5.2               700  2   0.01 0.1 0.1 TiO.sub.2                                                                          3.0 13        45                                                                              21                                                                              -9.1      -8.1                                                                              -4.8               700  2   0.01 3.0 0.1 TiO.sub.2                                                                          0.1 15        42                                                                              20                                                                              -8.5      -9.3                                                                              -4.6               700  2   0.01 0.1 3.0 TiO.sub.2                                                                          0.6 14        45                                                                              22                                                                              -9.3      -10 -4.7               700  2   0.01 3.0 3.0 TiO.sub.2                                                                          0.1 15        45                                                                              21                                                                              -8.5      -9.5                                                                              -4.8               700  2   0.01 0.1 3.0 TiO.sub.2                                                                          3.0 12        46                                                                              20                                                                              -8.6      -10 -4.6               700  2   0.01 3.0 0.1 TiO.sub.2                                                                          3.0 14        45                                                                              20                                                                              -9.1      -8.2                                                                              -4.6               700  2   10.0 3.0 0.1 TiO.sub.2                                                                          0.1 10        43                                                                              21                                                                              -9.3      -8.1                                                                              -4.7               700  2   10.0 0.1 3.0 TiO.sub.2                                                                          0.1 9         43                                                                              20                                                                              -8.7      -10 -4.7               700  2   10.0 0.1 0.1 TiO.sub.2                                                                          3.0 5         42                                                                              20                                                                              -8.1      -9.5                                                                              -5.0               700  2   0.01 3.0 3.0 TiO.sub.2                                                                          3.0 13        45                                                                              22                                                                              -9.4      -9.7                                                                              -5.0               700  2   10.0 0.1 3.0 TiO.sub.2                                                                          3.0 10        44                                                                              22                                                                              -9.8      -8.3                                                                              - 4.6              700  2   10.0 3.0 0.1 TiO.sub.2                                                                          3.0 4         40                                                                              20                                                                              -9.9      -9.6                                                                              -4.3               700  2   10.0 3.0 3.0 TiO.sub.2                                                                          0.1 14        42                                                                              21                                                                              -10       -10 -4.1               700  2   10.0 3.0 3.0 TiO.sub.2                                                                          3.0 15        41                                                                              21                                                                              -10       -10 -3.8               500   10 0.5  0.5 0.5 TiO.sub.2                                                                          0.5 12        40                                                                              20                                                                              -17.2     -6.2                                                                              -3.7               700  2   0.5  0.5 0.5 TiO.sub.2                                                                          0.5 8         43                                                                              24                                                                              -6.1      -5.1                                                                              -3.9               800  2   0.5  0.5 0.5 TiO.sub.2                                                                          0.5 8         47                                                                              25                                                                              -6.3      -5.1                                                                              -4.0               1000 1   0.5  0.5 0.5 TiO.sub.2                                                                          0.5 15        40                                                                              20                                                                              -17.2     -5.9                                                                              -4.1               700  2   0.01 0.1 0.1 BaO  0.01                                                                              42        30                                                                              20                                                                              -10       -10 -4.3               700  2   10.0 3.0 3.0 BaO  5.0 70        30                                                                              20                                                                              -9.1      -9.8                                                                              -4.2               500   10 0.5  0.5 0.5 BaO  0.5 38        31                                                                              21                                                                              -7.5      -8.5                                                                              -3.8               700  2   0.5  0.5 0.5 BaO  0.5 25        36                                                                              26                                                                              -5.0      -5.1                                                                              -3.1               1000 1   0.5  0.5 0.5 BaO  0.5 40        30                                                                              21                                                                              -8.2      -                                                                                 -3.9               700  2   0.01 0.1 0.1 Cr.sub.2 O.sub.3                                                                   0.01                                                                              48        28                                                                              20                                                                              --500     -9.9                                                                              -4.9               700  2   10.0 3.0 3.0 Cr.sub.2 O.sub.3                                                                   5.0 50        29                                                                              20                                                                              -9.4      -8.9                                                                              -4.3               500   10 0.5  0.5 0.5 Cr.sub.2 O.sub.3                                                                   0.1 68        35                                                                              22                                                                              -9.1      -9.3                                                                              -4.2               700  2   0.5  0.5 0.5 Cr.sub.2 O.sub.3                                                                   0.1 60        38                                                                              25                                                                              -6.0      -5.5                                                                              -3.0               800  2   0.5  0.5 0.5 Cr.sub.2 O.sub.3                                                                   0.1 62        38                                                                              25                                                                              -6.1      -5.3                                                                              -2.8               1000 1   0.50 0.5 0.5 Cr.sub.2 O.sub.3                                                                   0.1 70        35                                                                              23                                                                              -9.8      -8.7                                                                              -4.0               700  2   0.01 0.1 0.1 NiO  0.01                                                                              68        38                                                                              20                                                                              -8.5      -9.5                                                                              -3.8               700  2   10.0 3.0 3.0 NiO  5.0 52        35                                                                              21                                                                              -8.3      -9.1                                                                              -4.2               500   10 0.5  0.5 0.5 NiO  0.5 35        40                                                                              23                                                                              -9.2      -9.0                                                                              -4.1               700  2   0.5  0.5 0.5 NiO  0.5 22        42                                                                              26                                                                              -5.1      -5.0                                                                              -2.8               800  2   0.5  0.5 0.5 NiO  0.5 20        42                                                                              26                                                                              -5.5      -4.9                                                                              -2.5               1000 1   0.5  0.5 0.5 NiO  0.5 21        40                                                                              24                                                                              -8.7      -8.1                                                                              -3.9               700  2   0.01 0.1 0.1 B.sub.2 O.sub.3                                                                    0.01                                                                              70        32                                                                              20                                                                              -8.5      -9.5                                                                              -4.3               700  2   10.0 3.0 3.0 B.sub.2 O.sub.3                                                                    10.0                                                                              55        31                                                                              20                                                                              -8.1      -9.1                                                                              -4.1               500   10 0.5  0.5 0.5 B.sub.2 O.sub.3                                                                    0.5 68        32                                                                              21                                                                              -7.5      -8.1                                                                              -3.7               700  2   0.5  0.5 0.5 B.sub.2 O.sub.3                                                                    0.5 50        35                                                                              25                                                                              -5.1      -5.9                                                                              -2.1               800  2   0.5  0.5 0.5 B.sub.2 O.sub.3                                                                    0.5 52        36                                                                              25                                                                              -5.3      -5.7                                                                              -2.0               1000 1   0.5  0.5 0.5 B.sub.2 O.sub.3                                                                    0.5 70        30                                                                              22                                                                              -9.1      -8.1                                                                              -3.8               700  2   0.5  0.5 0.5 TiO.sub.2                                                                          0.01                                                                              75        35                                                                              17                                                                              -7.5      -8.1                                                                              -3.2                                     BaO  0.01                                               700  2   0.5  0.5 0.5 TiO.sub.2                                                                          1.0 20        40                                                                              20                                                                              -7.2      -7.9                                                                              -3.0                                     BaO  0.5                                                700  2   0.5  0.5 0.5 TiO.sub.2                                                                          0.5 32        40                                                                              20                                                                              -7.8      -7.6                                                                              -3.2                                     BaO  5.0                                                700  2   0.5  0.5 0.5 TiO.sub.2                                                                          0.1 30        40                                                                              20                                                                              -8.2      -7.2                                                                              -3.1                                     BaO  0.5                                                700  2   0.5  0.5 0.5 TiO.sub.2                                                                          3.0 30        40                                                                              19                                                                              -8.3      -7.5                                                                              -3.2                                     BaO  0.5                                                500   10 0.5  0.5 0.5 TiO.sub.2                                                                          0.5 25        45                                                                              22                                                                              -7.5      -8.1                                                                              -2.6                                     BaO  0.5                                                700  2   0.5  0.5 0.5 TiO.sub.2                                                                          0.5 15        50                                                                              25                                                                              -5.1      -5.3                                                                              -1.7                                     BaO  0.5                                                800  2   0.5  0.5 0.5 TiO.sub.2                                                                          0.5 16        50                                                                              24                                                                              -5.5      -5.4                                                                              -1.8                                     BaO  0.5                                                1000 1   0.5  0.5 0.5 TiO.sub.2                                                                          0.5 28        44                                                                              23                                                                              -7.5      -6.9                                                                              -2.3                                     BaO  0.5                                                500   10 0.5  0.5 0.5 TiO.sub.2                                                                          0.5 30        50                                                                              25                                                                              -7.2      -8.1                                                                              -2.7                                     Cr.sub.2 O.sub.3                                                                   0.5                                                700  2   0.5  0.5 0.5 TiO.sub.2                                                                          0.5 12        60                                                                              30                                                                              -6.0      -5.9                                                                              -1.6                                     Cr.sub.2 O.sub.3                                                                   0.5                                                800  2   0.5  0.5 0.5 TiO.sub.2                                                                          0.5 10        60                                                                              30                                                                              -6.1      -5.4                                                                              -1.7                                     Cr.sub.2 O.sub.3                                                                   0.5                                                1000 5   0.5  0.5 0.5 TiO.sub.2                                                                          0.5 28        50                                                                              25                                                                              -7.8      -7.9                                                                              -2.8                                     Cr.sub.2 O.sub.3                                                                   0.5                                                500   10 0.5  0.5 0.5 TiO.sub.2                                                                          0.5 25        40                                                                              20                                                                              -8.1      -8.5                                                                              -2.9                                     BaO.sub.3                                                                          0.5                                                700  2   0.5  0.5 0.5 TiO.sub.2                                                                          0.5 13        45                                                                              25                                                                              -5.1      -5.8                                                                              -1.7                                     B.sub.2 O.sub.3                                                                    0.5                                                800  2   0.5  0.5 0.5 TiO.sub.2                                                                          0.5 14        46                                                                              25                                                                              -5.4      -5.2                                                                              -1.8                                     B.sub.2 O.sub.3                                                                    0.5                                                1000 1   0.5  0.5 0.5 TiO.sub.2                                                                          0.5 30        41                                                                              21                                                                              -7.9      -8.1                                                                              -2.8                                     B.sub.2 O.sub.3                                                                    0.5                                                500   10 0.5  0.5 0.5 TiO.sub. 2                                                                         0.5 43        35                                                                              18                                                                              -8.1      -7.9                                                                              -3.0                                     NiO  0.5                                                700  2   0.5  0.5 0.5 TiO.sub.2                                                                          0.5 15        40                                                                              20                                                                              -5.3      -5.1                                                                              -1.6                                     NiO  0.5                                                800  2   0.5  0.5 0.5 TiO.sub.2                                                                          0.5 20        41                                                                              21                                                                              -5.2      -5.0                                                                              -1.6                                     NiO  0.5                                                1000 1   0.5  0.5 0.5 TiO.sub.2                                                                          0.5 38        37                                                                              19                                                                              -7.5      -8.2                                                                              -2.8                                     NiO  0.5                                                500   10 0.5  0.5 0.5 Cr.sub.2 O.sub.3                                                                   0.5 68        38                                                                              19                                                                              -8.7      -8.3                                                                              -3.1                                     B.sub.2 O.sub.3                                                                    0.5                                                700  2   0.5  0.5 0.5 Cr.sub.2 O.sub.3                                                                   0.5 50        45                                                                              25                                                                              -5.0      -5.3                                                                              -1.5                                     B.sub.2 O.sub.3                                                                    0.5                                                800  2   0.5  0.5 0.5 Cr.sub.2 O.sub.3                                                                   0.5 48        46                                                                              26                                                                              -5.1      -5.0                                                                              -1.3                                     B.sub.2 O.sub.3                                                                    0.5                                                1000 1   0.5  0.5 0.5 Cr.sub.2 O.sub.3                                                                   0.5 65        40                                                                              20                                                                              -6.5      -8.4                                                                              -3.0                                     B.sub.2 O.sub.3                                                                    0.5                                                500   10 0.5  0.5 0.5 Cr.sub.2 O.sub.3                                                                   0.5 58        38                                                                              19                                                                              -7.2      -8.1                                                                              -3.0                                     NiO  0.5                                                700  2   0.5  0.5 0.5 Cr.sub.2 O.sub.3                                                                   0.5 38        42                                                                              21                                                                              -5.5      -5.7                                                                              -1.7                                     NiO  0.5                                                800  2   0.5  0.5 0.5 Cr.sub.2 O.sub.3                                                                   0.5 37        43                                                                              21                                                                              -5.6      -5.8                                                                              -1.6                                     NiO  0.5                                                1000 1   0.5  0.5 0.5 Cr.sub.2 O.sub.3                                                                   0.5 69        37                                                                              18                                                                              -6.9      -7.9                                                                              -2.9                                     NiO  0.5                                                500   10 0.5  0.5 0.5 BaO  0.5 65        40                                                                              20                                                                              -6.5      -6.8                                                                              -2.9                                     Cr.sub.2 O.sub.3                                                                   0.5                                                700  2   0.5  0.5 0.5 BaO  0.5 32        46                                                                              25                                                                              -5.0      -5.3                                                                              -1.8                                     Cr.sub.2 O.sub.3                                                                   0.5                                                800  2   0.5  0.5 0.5 BaO  0.5 35        45                                                                              24                                                                              -5.1      -4.9                                                                              -1.9                                     Cr.sub.2 O.sub.3                                                                   0.5                                                1000 1   0.5  0.5 0.5 BaO  0.5 55        39                                                                              21                                                                              - 6.4     -6.2                                                                              -3.0                                     Cr.sub.2 O.sub.3                                                                   0.5                                                500   10 0.5  0.5 0.5 B.sub.2 O.sub.3                                                                    0.5 55        33                                                                              20                                                                              -6.2      -6.9                                                                              -2.8                                     NiO  0.5                                                700  2   0.5  0.5 0.5 B.sub.2 O.sub.3                                                                    0.5 20        40                                                                              24                                                                              -5.1      -5.3                                                                              -1.4                                     NiO  0.5                                                800  2   0.5  0.5 0.5 B.sub.2 O.sub.3                                                                    0.5 21        40                                                                              24                                                                              -5.0      -5.1                                                                              -1.7                                     NiO  0.5                                                1000 1   0.5  0.5 0.5 B.sub.2 O.sub.3                                                                    0.5 62        35                                                                              21                                                                              -6.8      -7.2                                                                              -2.9                                     NiO  0.5                                                500   10 0.5  0.5 0.5 BaO  0.5 80        38                                                                              19                                                                              -7.2      -8.0                                                                              -2.6                                     B.sub.2 O.sub.3                                                                    0.5                                                700  2   0.5  0.5 0.5 BaO  0.5 65        42                                                                              21                                                                              -5.0      -5.1                                                                              -1.5                                     B.sub.2 O.sub.3                                                                    0.5                                                800  2   0.5  0.5 0.5 BaO  0.5 60        43                                                                              22                                                                              -4.9      -4.8                                                                              -1.4                                     B.sub.2 O.sub.3                                                                    0.5                                                1000 1   0.5  0.5 0.5 BaO  0.5 72        39                                                                              20                                                                              -6.9      -7.7                                                                              -2.4                                     B.sub.2 O.sub.3                                                                    0.5                                                500   10 0.5  0.5 0.5 BaO  0.5 65        42                                                                              21                                                                              -6.7      -7.2                                                                              -2.5                                     NiO  0.5                                                700  2   0.5  0.5 0.5 BaO  0.5 43        47                                                                              25                                                                              -5.4      -5.7                                                                              -1.6                                     NiO  0.5                                                800  2   0.5  0.5 0.5 BaO  0.5 40        46                                                                              25                                                                              -5.5      -5.3                                                                              -1.8                                     NiO  0.5                                                1000 1   0.5  0.5 0.5 BaO  0.5 59        41                                                                              20                                                                              -6.9      -7.8                                                                              -2.3                                     NiO  0.5                                                                      TiO.sub.2                                                                          0.5                                                500   10 0.5  0.5 0.5 BaO  0.5 42        42                                                                              21                                                                              - 4.7     -2.0                                                                              -1.9                                     Cr.sub.2 O.sub.3                                                                   0.5                                                                      TiO.sub.2                                                                          0.5                                                700  2   0.5  0.5 0.5 BaO  0.5 15        48                                                                              25                                                                              -2.5      -0.8                                                                              -0.8                                     Cr.sub.2 O.sub.3                                                                   0.5                                                                      TiO.sub.2                                                                          0.5                                                800  2   0.5  0.5 0.5 BaO  0.5 16        49                                                                              24                                                                              -2.6      -0.9                                                                              -0.9                                     Cr.sub.2 O.sub.3                                                                   0.5                                                                      TiO.sub.2                                                                          0.5                                                1000 1   0.5  0.5 0.5 BaO  0.5 29        41                                                                              20                                                                              -4.5      -2.0                                                                              -1.8                                     Cr.sub.2 O.sub.3                                                                   0.5                                                                      TiO.sub.2                                                                          0.5                                                500   10 0.5  0.5 0.5 BaO  0.5 18        45                                                                              22                                                                              -4.6      -2.1                                                                              -1.5                                     B.sub.2 O.sub.3                                                                    0.5                                                                      TiO.sub.2                                                                          0.5                                                700  2   0.5  0.5 0.5 BaO  0.5 9         50                                                                              26                                                                              -2.4      -0.8                                                                              -0.7                                     B.sub.2 O.sub.3                                                                    0.5                                                                      TiO.sub.2                                                                          0.5                                                800  2   0.5  0.5 0.5 BaO  0.5 10        49                                                                              27                                                                              -2.5      -0.7                                                                              -0.8                                     B.sub.2 O.sub.3                                                                    0.5                                                                      TiO.sub.2                                                                          0.5                                                1000 1   0.5  0.5 0.5 BaO  0.5 20        40                                                                              21                                                                              -4.1      -2.2                                                                              -1.6                                     B.sub.2 O.sub.3                                                                    0.5                                                                      TiO.sub.2                                                                          0.5                                                500   10 0.5  0.5 0.5 BaO  0.5 45        40                                                                              23                                                                              -4.3      -2.5                                                                              -1.8                                     NiO  0.5                                                                      TiO.sub.2                                                                          0.5                                                700  2   0.5  0.5 0.5 BaO  0.5 20        45                                                                              26                                                                              -2.8      -1.2                                                                              -0.9                                     NiO  0.5                                                                      TiO.sub.2                                                                          1.0                                                800  2   0.5  0.5 0.5 BaO  0.5 23        46                                                                              27                                                                              -2.4      -1.1                                                                              -1.0                                     NiO  0.5                                                                      TiO.sub.2                                                                          1.0                                                1000 1   0.5  0.5 0.5 BaO  0.5 50        41                                                                              24                                                                              -4.1      -2.4                                                                              -1.9                                     NiO  0.5                                                                      BaO  0.5                                                500   10 0.5  0.5 0.5 B.sub.2 O.sub.3                                                                    0.5 42        40                                                                              23                                                                              -4.3      -3.2                                                                              -2.2                                     NiO  0.5                                                                      BaO  0.5                                                700  2   0.5  0.5 0.5 B.sub.2 O.sub.3                                                                    0.5 25        46                                                                              27                                                                              -2.5      -1.3                                                                              -0.9                                     NiO  0.5                                                                      BaO  0.5                                                800  2   0.5  0.5 0.5 B.sub.2 O.sub.3                                                                    0.5 23        45                                                                              28                                                                              -2.4      -1.5                                                                              -1.0                                     NiO  0.5                                                                      BaO  0.5                                                1000 1   0.5  0.5 0.5 B.sub.2 O.sub.3                                                                    0.5 40        41                                                                              24                                                                              -4.5      -3.0                                                                              -2.0                                     NiO  0.5                                                                      B.sub.2 O.sub.3                                                                    0.5                                                500   10 0.5  0.5 0.5 NiO  0.5 32        40                                                                              22                                                                              -4.5      -3.9                                                                              -2.0                                     Cr.sub.2 O.sub.3                                                                   0.5                                                                      B.sub.2 O.sub.3                                                                    0.5                                                700  2   0.5  0.5 0.5 NiO  0.5 10        44                                                                              27                                                                              -2.2      -1.8                                                                              -1.1                                     Cr.sub.2 O.sub.3                                                                   0.5                                                                      B.sub.2 O.sub.3                                                                    0.5                                                800  2   0.5  0.5 0.5 NiO  0.5 15        45                                                                              26                                                                              -2.4      -1.5                                                                              -0.9                                     Cr.sub.2 O.sub.3                                                                   0.5                                                                      B.sub.2 O.sub.3                                                                    0.5                                                1000 1   0.5  0.5 0.5 NiO  0.5 28        40                                                                              21                                                                              -4.6      -3.8                                                                              -2.3                                     Cr.sub.2 O.sub.3                                                                   0.5                                                                      TiO.sub.2                                                                          0.5                                                500   10 0.5  0.5 0.5 NiO  0.5 35        36                                                                              20                                                                              -3.4      -3.2                                                                              -2.6                                     Cr.sub.2 O.sub.3                                                                   0.5                                                                      TiO.sub.2                                                                          0.5                                                700  2   0.5  0.5 0.5 NiO  0.5 22        42                                                                              26                                                                              -0.8      -1.2                                                                              -0.3                                     Cr.sub.2 O.sub.3                                                                   0.5                                                                      TiO.sub.2                                                                          0.5                                                800  2   0.5  0.5 0.5 NiO  0.5 21        41                                                                              25                                                                              -0.8      -1.1                                                                              -0.2                                     Cr.sub.2 O.sub.3                                                                   0.5                                                                      TiO.sub.2                                                                          0.5                                                1000 1   0.5  0.5 0.5 NiO  0.5 40        37                                                                              21                                                                              -3.3      -3.5                                                                              -2.5                                     Cr.sub.2 O.sub.3                                                              BaO  0.5                                                500   10 0.5  0.5 0.5 NiO  0.5 45        38                                                                              20                                                                              -4.8      -3.3                                                                              -2.7                                     Cr.sub.2 O.sub.3                                                                   0.5                                                                      BaO  0.5                                                700  2   0.5  0.5 0.5 NiO  0.5 22        42                                                                              25                                                                              -1.5      -0.9                                                                              -0.4                                     Cr.sub.2 O.sub.3                                                                   0.5                                                                      BaO  0.5                                                800  2   0.5  0.5 0.5 NiO  0.5 21        42                                                                              25                                                                              -1.7      -0.8                                                                              -0.8                                     Cr.sub.2 O.sub.3                                                                   0.5                                                                      BaO  0.5                                                1000 1   0.5  0.5 0.5 NiO  0.5 38        37                                                                              21                                                                              -4.6      -2.9                                                                              -2.5                                     Cr.sub.2 O.sub.3                                                                   0.5                                                                      TiO.sub.2                                                                          0.5                                                500   10 0.5  0.5 0.5 NiO  0.5 30        40                                                                              20                                                                              -4.1      -3.3                                                                              -2.5                                     B.sub.2 O.sub.3                                                                    0.5                                                                      TiO.sub.2                                                                          0.5                                                700  2   0.5  0.5 0.5 NiO  0.5 15        46                                                                              25                                                                              -1.0      -0.5                                                                              -1.5                                     B.sub.2 O.sub.3                                                                    0.5                                                                      TiO.sub.2                                                                          0.5                                                800  2   0.5  0.5 0.5 NiO  0.5 12        47                                                                              25                                                                              -1.2      -0.7                                                                              -1.2                                     B.sub.2 O.sub.3                                                                    0.5                                                                      TiO.sub.2                                                                          0.5                                                1000 1   0.5  0.5 0.5 NiO  0.5 28        41                                                                              21                                                                              -4.0      -3.2                                                                              -2.8                                     B.sub.2 O.sub.3                                                                    0.5                                                                      TiO.sub.2                                                                          0.5                                                500   10 0.5  0.5 0.5 B.sub.2 O.sub.3                                                                    0.5 48        40                                                                              21                                                                              -5.0      -2.1                                                                              -3.5                                     Cr.sub.2 O.sub.3                                                                   0.5                                                                      TiO.sub.2                                                                          1.0                                                700  2   0.5  0.5 0.5 B.sub.2 O.sub.3                                                                    0.5 38        48                                                                              27                                                                              -2.5      -0.3                                                                              -1.1                                     Cr.sub.2 O.sub.3                                                                   0.5                                                                      TiO  1.0                                                800  2   0.5  0.5 0.5 B.sub.2 O.sub.3                                                                    0.5 37        49                                                                              28                                                                              -2.1      -0.3                                                                              -1.0                                     Cr.sub.2 O.sub.3                                                                   0.5                                                                      TiO.sub.2                                                                          1.0                                                1000 1   0.5  0.5 0.5 B.sub.2 O.sub.3                                                                    0.5 50        41                                                                              22                                                                              -4.8      -2.1                                                                              -3.7                                     Cr.sub.2 O.sub.3                                                                   0.5                                                                      BaO  0.5                                                500   10 0.5  0.5 0.5 NiO  0.5 58        40                                                                              27                                                                              -4.5      -1.5                                                                              -1.8                                     Cr.sub.2 O.sub.3                                                                   0.5                                                                      BaO  0.5                                                700  2   0.5  0.5 0.5 NiO  0.5 40        44                                                                              31                                                                              -2.1      -0.6                                                                              -0.7                                     Cr.sub.2 O.sub.3                                                                   0.5                                                                      BaO  0.5                                                800  2   0.5  0.5 0.5 NiO  0.5 42        45                                                                              30                                                                              -2.2      -0.5                                                                              -0.8                                     Cr.sub.2 O.sub.3                                                                   0.5                                                                      BaO  0.5                                                1000 1   0.5  0.5 0.5 NiO  0.5 65        40                                                                              26                                                                              -4.8      -1.2                                                                              -1.5                                     Cr.sub.2 O.sub.3                                                                   0.5                                                                      TiO.sub.2                                                                          0.5                                                500   10 0.5  0.5 0.5 BaO  0.5 50        41                                                                              30                                                                              -2.5      +0.1                                                                              +0.1                                     NiO  0.5                                                                      Cr.sub.2 O.sub.3                                                                   0.5                                                                      TiO  0.5                                                700  2   0.5  0.5 0.5 BaO  0.5 38        45                                                                              32                                                                              -1.9      +1.8                                                                              +2.0                                     NiO  0.5                                                                      Cr.sub.2 O.sub.3                                                                   0.5                                                                      TiO.sub.2                                                                          0.5                                                800  2   0.5  0.5 0.5 BaO  0.5 35        45                                                                              32                                                                              -1.8      +1.9                                                                              +2.0                                     NiO  0.5                                                                      Cr.sub.2 O.sub.3                                                                   0.5                                                                      TiO.sub.2                                                                          0.5                                                1000 1   0.5  0.5 0.5 BaO  0.5 48        40                                                                              30                                                                              -2.4      +0.2                                                                              +0.5                                     NiO  0.5                                                                      Cr.sub.2 O.sub.3                                                                   0.5                                                                      TiO.sub.2                                                                          0.5                                                500   10 0.5  0.5 0.5 NiO  0.5 50        43                                                                              30                                                                              -1.3      +0.5                                                                              +0.2                                     Cr.sub.2 O.sub.3                                                                   0.5                                                                      B.sub.2 O.sub.3                                                                    0.5                                                700  2   0.5  0.5 0.5 NiO  0.5 21        46                                                                              31                                                                              -0.2      +1.1                                                                              +1.3                                     Cr.sub.2 O.sub.3                                                                   0.5                                                                      B.sub.2 O.sub.3                                                                    0.5                                                                      TiO.sub.2                                                                          0.5                                                800  2   0.5  0.5 0.5 NiO  0.5 25        46                                                                              31                                                                              -0.1      +1.2                                                                              +1.5                                     Cr.sub.2 O.sub.3                                                                   0.5                                                                      B.sub.2 O.sub.3                                                                    0.5                                                                      TiO.sub.2                                                                          0.5                                                1000 1   0.5  0.5 0.5 NiO  0.5 48        42                                                                              30                                                                              -1.8      +0.3                                                                              +0.1                                     Cr.sub.2 O.sub.3                                                                   0.5                                                                      B.sub.2 O.sub.3                                                                    0.5                                                                      TiO.sub.2                                                                          0.5                                                500   10 0.5  0.5 0.5 BaO  0.5 25        35                                                                              30                                                                              -2.0      +0.2                                                                              +0.1                                     NiO  0.5                                                                      B.sub.2 O.sub.3                                                                    0.5                                                                      TiO.sub.2                                                                          0.5                                                700  2   0.5  0.5 0.5 BaO  0.5 13        38                                                                              31                                                                              -1.4      +1.2                                                                              +1.1                                     NiO  0.5                                                                      B.sub.2 O.sub.3                                                                    0.5                                                                      TiO.sub.2                                                                          0.5                                                800  2   0.5  0.5 0.5 BaO  0.5 15        40                                                                              30                                                                              -1.1      +1.5                                                                              +1.3                                     NiO  0.5                                                                      B.sub.2 O.sub.3                                                                    0.5                                                                      TiO.sub.2                                                                          0.5                                                1000 1   0.5  0.5 0.5 BaO  0.5 28        35                                                                              30                                                                              -1.8      +0.5                                                                              +0.1                                     NiO  0.5                                                                      B.sub.2 O.sub.3                                                                    0.5                                                                      TiO.sub.2                                                                          0.5                                                500   10 0.5  0.5 0.5 BaO  0.5 25        44                                                                              30                                                                              -1.8      +0.8                                                                              +0.3                                     Cr.sub.2 O.sub.3                                                                   0.5                                                                      B.sub.2 O.sub.3                                                                    0.5                                                700  2   0.5  0.5 0.5 BaO  0.5 13        47                                                                              32                                                                              -1.1      +2.8                                                                              + 1.3                                    Cr.sub.2 O.sub.3                                                                   0.5                                                                      B.sub.2 O.sub.3                                                                    0.5                                                                      TiO.sub.2                                                                          0.5                                                800  2   0.5  0.5 0.5 BaO  0.5 15        47                                                                              31                                                                              -1.2      +2.8                                                                              +1.2                                     Cr.sub.2 O.sub.3                                                                   0.5                                                                      B.sub.2 O.sub.3                                                                    0.5                                                                      TiO.sub.2                                                                          0.5                                                1000 1   0.5  0.5 0.5 BaO  0.5 30        45                                                                              30                                                                              -1.7      +0.2                                                                              +0.4                                     Cr.sub.2 O.sub.3                                                                   0.5                                                                      B.sub.2 O.sub.3                                                                    0.5                                                                      BaO  0.5                                                500   10 0.5  0.5 0.5 NiO  0.5 20        40                                                                              30                                                                              -1.5      +1.5                                                                              +0.2                                     Cr.sub.2 O.sub.3                                                                   0.5                                                                      B.sub.2 O.sub.3                                                                    0.5                                                700  2   0.5  0.5 0.5          15        42                                                                              31                                                                              -1.0      +3.0                                                                              +1.5                                     BaO  0.5                                                                      NiO  0.5                                                                      Cr.sub.2 O.sub.3                                                                   0.5                                                                      B.sub.2 O.sub.3                                                                    0.5                                                800  2   0.5  0.5 0.5          13        43                                                                              30                                                                              -1.1      +3.3                                                                              +1.4                                     BaO  0.5                                                                      NiO  0.5                                                                      Cr.sub.2 O.sub.3)                                                                  0.5                                                                      B.sub.2 O.sub.3                                                                    0.5                                                1000 1   0.5  0.5 0.5          21        40                                                                              30                                                                              -1.8      +0.5                                                                              +0.3                                     BaO  0.5                                                                      NiO  0.5                                                                      Cr.sub.2 O.sub.3                                                                   0.5                                                                      B.sub.2 O.sub.3                                                                    0.5                                                500   10 0.5  0.5 0.5          28        50                                                                              30                                                                              -0.8      +2.0                                                                              +1.2                                     TiO.sub.2                                                                          0.5                                                                      BaO  0.5                                                                      NiO  0.5                                                                      Cr.sub.2 O.sub.3                                                                   0.5                                                                      B.sub.2 O.sub.3                                                                    0.5                                                700  2   0.5  0.5 0.5          12        50                                                                              30                                                                              -0.5      +5.0                                                                              +5.2                                     TiO.sub.2                                                                          0.5                                                                      BaO  0.5                                                                      NiO  0.5                                                                      Cr.sub.2 O.sub.3                                                                   0.5                                                                      B.sub.2 O.sub.3                                                                    0.5                                                800  2   0.5  0.5 0.5          15        50                                                                              30                                                                              -0.5      +5.0                                                                              +5.2                                     TiO.sub.2                                                                          0.5                                                                      BaO  0.5                                                                      NiO  0.5                                                                      Cr.sub.2 O.sub.3                                                                   0.5                                                                      B.sub.2 O.sub.3                                                                    0.5                                                1000 1   0.5  0.5 0.5          20        50                                                                              30                                                                              -0.5      +2.0                                                                              +1.0                                     TiO.sub.2                                                                          0.5                                                                      BaO  0.5                                                                      NiO  0.5                                                                      Cr.sub.2 O.sub.3                                                                   0.5                                                                      B.sub.2 O.sub.3                                                                    0.5                                                __________________________________________________________________________

EXAMPLE 6

The resistors of Examples 2, 3, 4 and 5 were tested in accordance with amethod widely used in testing electronic component parts. A heatingcycle test was carried out by repeating 5 times the cycle in which theresistors are kept at 85°C ambient temperature for 30 minutes, cooledrapidly to -20°C and then kept at such temperature for 30 minutes. Ahumidity test was carried out at 40°C and 95% relative humidity for 1000hrs. Table 8 shows the average change rates of the C-value and n-valueof the resistors after the heating cycle test and the humidity test. Itis easily understood that each sample has a small change rate.

                  Table 6                                                         ______________________________________                                                 Heating cycle Test                                                                            Humidity Test                                        Sample No.                                                                             (%)             (%)                                                         ΔC                                                                            Δn.sub.1                                                                        Δn.sub.2                                                                        ΔC                                                                            Δn.sub.1                                                                      Δn.sub.2                       ______________________________________                                        Example 2                                                                              -4.5    -6.5    -6.2  -5.3  -6.6  -6.1                               Example 3                                                                              -3.5    -4.3    -4.4  -3.2  -4.1  -4.4                               Example 4                                                                              -0.3    -0.2    -0.3  -1.3  -1.5  -1.6                               Example 5                                                                              -0.4    -0.5    -0.7  -1.8  -1.7  -2.0                               ______________________________________                                    

What is claimed is:
 1. In a process for making a bulk-typevoltage-dependent resistor in which zinc oxide (ZnO) powder andadditives are admixed to form a sintered body composition having as themain constituent, zinc oxide, and in which the mixture is formed into aresistor body, the body is sintered, and electrodes are applied to theopposite surfaces of the sintered body, the improvement comprising thestep of, prior to sintering and admixture with said additives,heat-treating the zinc oxide powder at a temperature of from 500° to1000°C.
 2. The improvement according to claim 1, in which saidtemperature for heat-treating the zinc oxide powder is from 700° to800°C.
 3. The improvement according to claim 1 further comprising, inthe step of mixing the sintered body composition, mixing together as amain constituent, 99.98 to 80 mole percent of zinc oxide (ZnO), and, asadditives 0.01 to 10 mole percent of bismuth oxide (Bi₂ O₃), and 0.01 to10 mole percent, in total, of two members selected from the groupconsisting of cobalt oxide (CoO), uranium oxide (UO₂), manganese oxide(MnO), antimony oxide (Sb₂ O₃), barium oxide (BaO), strontium oxide(SrO) and lead oxide (PbO).
 4. The improvement according to claim 3, inwhich said temperature for heat-treating the zinc oxide powder is from700°C to 800°C.
 5. The improvement according to claim 1 which comprisesmixing 0.01 to 10 mole percent of bismuth oxide (Bi₂ O₃), 0.1 to 3.0mole percent of cobalt oxide (CoO), 0.1 to 3.0 mole percent of manganeseoxide (MnO), at least one member selected from the group consisting of0.01 to 8.0 mole percent of antimony oxide (Sb₂ O₃), 0.1 to 5.0 molepercent of tin oxide (SnO₂), and 0.01 to 10 mole percent of siliconoxide (SiO₂), and at least one member selected from the group consistingof 0.01 to 5.0 mole percent of chromium oxide (Cr₂ O₃), 0.01 to 5.0 molepercent of nickel oxide (NiO) and as the remainder, zinc oxide (ZnO). 6.The improvement according to claim 5 in which said temperature forheat-treating the zinc oxide powder is from 700°C to 800°C.
 7. Theimprovement according to claim 1, which comprises mixing 0.01 to 10.0mole percent of bismuth oxide (Bi₂ O₃), 0.1 to 3.0 mole percent ofcobalt oxide (CoO), 0.1 to 3.0 mole percent of manganese oxide (MnO) andat least one member selelcted from the group consisting of 0.1 to 3.0mole percent of titanium oxide (TiO₂), 0.01 to 5.0 mole percent ofnickel oxide (NiO), 0.01 to 5.0 mole percent of chromium oxide (Cr₂ O₃),0.01 to 5.0 mole percent of barium oxide (BaO) and 0.01 to 5.0 molepercent of boron oxide (B₂ O₃) and as the remainder, zinc oxide (ZnO).8. The improvement according to claim 7 in which said temperature forheat-treating the zinc oxide powder is from 700°C to 800°C.
 9. In a bulktype voltage-dependent resistor produced by admixing zinc oxide (ZnO)powder and additives to form a sintered body composition having as themain constituent the zinc oxide, and wherein the mixture is formed intoa resistor body, the body is sintered, and electrodes are applied toopposite surfaces of the sintered body, the improvement in the processcomprising the step of, prior to sintering and admixing with saidadditives, heat-treating the zinc oxide powder at a temperature of from500° to 1000°C.
 10. A voltage-dependent resistor according to claim 9 inwhich said temperature for heat-treating the zinc oxide powder is from700° to 800°C.
 11. A voltage-dependent resistor according to claim 9 inwhich the improved process further comprises, in the step of mixing thesintered body composition, mixing together as a main constituent, 99.98to 80 mole percent of zinc oxide (ZnO), and, as additives, 0.01 to 10mole percent of bismuth oxide (Bi₂ O₃), and 0.01 to 10 mole percent, intotal, of two members selected from the group consisting of cobalt oxide(CoO), uranium oxide (UO₂), manganese oxide (MnO), antimony oxide (Sb₂O₃), barium oxide (BaO), strontium oxide (SrO) and lead oxide (PbO). 12.A voltage-dependent resistor as claimed in claim 11 in which saidtemperature for heat-treating the zinc oxide powder is from 700° to800°C.
 13. A voltage-dependent resistor according to claim 9 in whichthe improved process further comprises in the step of mixing thesintered body composition, mixing together as a main constituent, zincoxide (ZnO), and, as additives, 0.01 to 10 mole percent of bismuth oxide(Bi₂ O₃), 0.1 to 3.0 mole percentage of cobalt oxide (CoO), 0.1 to 3.0mole percent of manganese oxide (MnO), at least one member selected fromthe group consisting of 0.01 to 8.0 mole percent of antimony oxide (Sb₂O₃), 0.1 to 5.0 mole percent of tin oxide (SnO₂), and 0.01 to 10 molepercent of silicon oxide (SiO₂), and at least one member selected fromthe group consisting of 0.01 to 5.0 mole percent of chromium oxide (Cr₂O₃), 0.01 to 5.0 mole percent of nickel oxide (NiO).
 14. Avoltage-dependent resistor as claimed in claim 13 in which saidtemperature for heat-treating the zinc oxide powder is from 700° to800°C.
 15. A voltage dependent resistor according to claim 9 in whichthe improved process further comprises, in the step of mixing thesintered body composition, mixing 0.01 to 10.0 mole percent of bismuthoxide (Bi₂ O₃), 0.1 to 3.0 mole percent of cobalt oxide (CoO), 0.1 to3.0 mole percent of manganese oxide (MnO) and at least one memberselected from the group consisting of 0.1 to 3.0 mole percent of thetitanium oxide (TiO₂), 0.01 to 5.0 mole percent of nickel oxide (NiO),0.01 to 5.0 mole percent of chromium oxide (Cr₂ O₃), 0.01 to 5.0 molepercent of barium oxide (BaO) and 0.1 to 5.0 mole percent of boron oxide(B₂ O₃).
 16. A voltage-dependent resistor as claimed in claim 15 inwhich said temperature for heat-treating the zinc oxide powder is from700° to 800°C.